Nathan's lawnmower uses 2/3 of a tank of gas to cut three one-acre lawns. How many one-acre lawns can he cut with a full tank of gas?

Using the data you have given, it seems he can cut 1 and a half lawns on a third of a tank of gas. Taking this data, and multiplying it by 3, Nathans lawn mower can mow down 4 one-acre lawns, and a lawn that's half an acre. (Your answer is basically 4 lawns)