A square's side length is represented by 2x - 1.8. Its perimeter is 24 inches. Which equation represents the perimeter?
a. 4(2x - 1.8) = 24
b. 2(2x - 1.8) = 24
c. (2x - 1.8) = 12
d. 4(2x - 1.8) = 12