The general form of an equation in intercetp form is:

Where m is the change of y in function of x and b is the value of b when x is 0
In this situation you have:
y=C
x=r
m= 1.75 ( C increase 1.75 each r)
b= 7 (When there is not ride r=0 the admission fee is 7)
Then, you have the equation:

or C = 7 + 1.75r