Supply is exhausted in a day , means sales >= capacity.
Area under the curve f(x) gives the total probability P( x > Capacity) = 0.01
f(x) = 5 at x =0 and f(x) = 0 at x = 1. As x is > 0 (volume of sale) and x < 1, the integration limits are from C < x < 1.
Let 1 - x = t then - dx = dt