Acar travels 172 miles using 7 gallons of gas. at at that rate, how far can the car travel using 42 gallons of gas a.1,032 miles b.1,548 c.1,204 d.1,376

The answer is A. 1,032 miles. 
You divide 42 gallons by 7. This is because you know how many miles can be reached per 7 gallons. 
41
172
x  6

1032

When you divide 42/7 you get 6. You then take 6 and multiply it by 172. 6x2 is 12, you carry the one, 6x7 is 42, plus the 1 that you carried, so you get 43, you carry the 4, 6x1 is 6, and you add the 4 to get 10. This brings your answer to 1, 032.