I think the answer is -4x^-11x+13
Four? Isn't it stated in the question? Unless I am assuming wrong.
Answer:
Multiply the rate per hour by the number of hours (n) and add the deposit.
A)
Bike shop x: c = 2.75n + 3.00
Bike shop z: c = 1.75n + 7.00
B) to find when they will cost the same set the equations equal to each other and solve for n:
2.75n + 3.00 = 1.75n + 7.00
Subtract 3 from each side:
2.75n = 1.75n + 4.00
Subtract 1.75n from both sides:
1.00n = 4.00
Divide both sides by 1:
n = 4 hours
The equation of the line that you get is:

Where m is the slope and q is the y-intercept; then the slope of y=3x-12 is 3.