The answer is B. y = -1/5x +1/2.
EXPLANATION
First solve for the slope:

After finding the slope, look for the linear equation with the same value of m (parallel equation).
It goes 2, 4, 10, 20 euros
(1,2)
(2,4)
(5,10)
(10,20)
The result of dividing

by

is

with no remainder. Please check the step by step procedures in the picture attached.
We can conclude that:
The quotient of the division is

The remainder of the division is

The divisor is

The dividend is
First calculate after tax tire price
$390.60 / 4 = $97.65 after tax price per tire
take the $97.65 divided by 90
97.65 / 90 = 1.085
1.085 is the rate of tax he paid per tire