The greatest common factor is the greatest number that can divide the terms. The greatest number that can divide each term is 4, and the greatest power of x that can divide each term is x^2. This is because it can't be any number greater than 4 since that number would never be able to divide into 4. This is also the reason why x^2 is the greatest power possible. It cannot be greater than anything divisible by itself. Thus, you multiply 4 by x^2 and the answer is 4x^2.
The miles he traveled by plane is nine times greater than the miles traveled by automobile. If the total is 600 miles, then the total distance traveled by automobile would be 60 miles, making the total traveled by airplane 540 miles.
