Your friend has 5100 when he goes to the fair. He spends $10 to enter the fair and $20 on food. Rides at the fair cost $2 per ride. Which function can be used to determine how much money he has left over after x rides?
f(x) = -2x + 70
f(x) = 2x + 70
f(x) = -2x - 70
f(x) = -30% + $100