Your examples of "the fix was on" and "who fixed the World Series" use fix in a different sense than that of Question 3.1. In those sentences, it is meaning 7a from dictionary.com: "to influence the actions, outcome, or effect of by improper or illegal methods." In the question, taking a normal business sense, fix would usually have meaning 1a: "to make firm, stable, or stationary."
If we fix a time, we settle on a single agreed time.
If we fix a price, we set the price and intend not to change it.
If we fix a deadline, we commit to delivering results by a given target date.
You could also fix a forecast, in the sense that you declare this forecast to be complete and as accurate as possible and you're not going to change it further. This would be an uncommon thing to do for a weather forecast (you always get better accuracy as you get closer to the event), but it's more likely for a business forecast, where you have a planning horizon that must be met; in that case you might fix your forecast 90 days out, because that's when you have to place orders to your overseas suppliers; so in January, February, and March you adjust your forecast for July and improve it as much as possible, but at the end of March you place your orders supplies to arrive in July, and you can't change those based on improved forecasting information that you receive in mid-May.)
One other thing to note is that "price-fixing" as a phrase always means "illegally colluding with others to set a price that would normally not be viable." So you may wish to avoid "we fixed our prices" because of the possibility of misunderstanding.
"Fix" means to assure in an unscrupulous way the outcome of a contest. The White Sox, for example, were widely favored to win the World Series, meaning that gamblers could expect to collect a lot of money if they bet on the opposing team, the Cincinnati Reds, while ensuring that the White Sox would lose--much more than they would collect if they bet on the White Sox to win in legitimate fashion. So, the gamblers (Rothstein in particular) bribed several of the White Sox players to throw the Series (i.e., to lose intentionally).
Wrestling is fixed as well, but this is widely understood and provokes little outrage, because wrestling is seen as entertainment. The fixing of the World Series, the national pastime, was seen as an outrage.
Political contests are often thought to be fixed as well--Donald Trump has used this term repeatedly of late in disparanging Ted Cruz's collection of delegates in states in which he won fewer votes than Trump. The common expression is "the fix is in," meaning the game is rigged--the outcome has been assured even before the contest takes place.
Clearly, the one word that does not belong with "fix" is C, a forecast. Again, it might apply in the rare (and perhaps purely hypothetical) case of a bogus forecast being used to fool people into thinking the weather will be something other than what you know it will be, but this is a far-fetched example.
"Fix" as applied to the other words has an entirely different meaning. Fix a time = decide upon and set a time; fix a price = decide on and set a price; Fix a deadline = decide on and set a deadline. The meaning here is to "fasten (something) securely in a particular place or position."
"Fix" can also mean to repair, as in "fix the refrigerator--it's broken."