The martin family's truck gets an average of 25 miles per gallon. predict how many milrs they can drive using 7 gallons of gas.

Okay so on average if they can go 25 miles per gallon that would mean you could just multiply 25 and 7 to get 175. So on average they could go 175 miles on 7 gallons of gas. Keep in mind that the answer can and will change depending on traffic, how fast or slow they are going, and if they are traveling behind a big-rig that moves more air that would normally be putting pressure on the car to push out of the way  but the big-rig helps save gas but it can also waste more gas if they are driving slower then normal.
Sorry for the extra information once I start it's hard to stop. Any way I hope this helps.