(6x^4) + (15x^3)(y^2) + (3x^2)(y^3) is your answer
As we are looking at descending powers of x. Look at the powers of the x. In the first one (6x^4), the power is 4, and 4 is greater than the other numbers given (3 & 2). Therefore, the order given above is correct.
To find the number of miles driven on one gallon, divide 420 by 20. that would be 21. multiply 21 by 65 to find the number of miles you can drive with 65 gallons.
