The answer is a.
I hope this helped
It helps to think of a simpler problem. Let's say mpg is 20 and 10% higher on a smooth road.
How many miles will you get with one gallon on a regular road?
How many more miles will you get on a smooth road? 10% more, right? How much is that?
OK - so you've now solved a simpler problem. Use the exact some process to solve your, more complicated, problem.
I believe the answer is 6.
Here’s your answer! Have a good day