The problem statement reads:

Include a prototype method in class, which returns a message(msg) "car name(name) had travelled for distance(distance) miles".

Which should mean that the method actually uses return instead of printing to the console.

class Car {
  constructor(name, distance) {
    this.name = name;
    this.distance = distance;

  }
  lengthMiles() {
    return `${this.name} had travelled for ${this.distance} miles`;
//  ^^^^^^ --------------------------- using a return statement
  }                            //    |
}                              //    |
                               //    |
var car = new Car('Audi', 100);//    |
var msg = car.lengthMiles();   //    |
console.log(msg);// <----------------- printing the message here