Hey there! :)
All you have to do is divide "miles driven" by "gallons used" to find the unit rate and see which is the lowest.
A = 45 ÷ 3 = 15 m/g
B = 24 ÷ 2 = 12 m/g
C = 14 ÷ 1 = 14 m/g
D = 35 ÷ 4 = 8.75 m/g
The lowest is D
Your answer is truck D
Hope this helps :)