Sal wants to know if he has enough money to buy 4 gallons of gas. if he has $15, and each gallon of gas costs $3.29, which is a good estimate for whether sal will be able to afford 4 gallons of gas? $3 + $3 + $3 + $3 = 12, so sal can afford the gas. $4 + $4 + $4 + $4 = 16, so sal can afford the gas. $3 + $3 + $3 + $3 = 12, so sal cannot afford the gas. $4 + $4 + $4 + $4 = 16, so sal cannot afford the gas.