math
posted by kathy m. on .
Suppose that a certain municipality uses the equation y=3(x50)+30 to determine the fine assessed a car which exceeds the 50 mph speed limit. Let x=speed of the car (in mph) and y=corresponding fine in dollars.
a)What is the fine for traveling at 55 mph?
b)If the fine is $126, what is the speed of the car?
c)If car A travels at 60 mph and car B travels at 90 mph, then car B is traveling 50% faster than car A. However the fine for car B is what percent higher than that of car A?

i just really need help with c. i know a is $45 and b is 102 mph but i don't get c

I disagree with your b) answer of 102
3(x50) + 30 = 126
3(x50) = 96
x50 = 32
x = 32+50 = 82 mph
c) fine for A is 3(6050) + 30 = $60
fine for B is 3(9050) + 30 = $150
increase in speed = 30 mph
increase in fine = 15060 = $90
percentage increase = 90/60 = 1.5 or 150% increase in the fine. 
yeah, i found out b was wrong after working it out again, but thanks so much for explaining c~