We can now say that the work required to move this layer is about W = 78,400 ∫₀⁵ (5x - x²) dx. What is the correct expression for the total work required?

a) W = 78,400 ∫₀⁵ (5x - x²) dx
b) W = 78,400x dx
c) W = 78,400 ∫₀⁵ (5 - x) dx
d) W = 78,400 ∫₀⁵ (x - 5) dx