Imagine slicing through a sphere with a plane (sheet of paper). The smaller piece produced is called a spherical cap. Its volume is V = πh² (3r - h)/3, where r is the radius of the sphere and h is the thickness of the cap. 

a. Find dr/dh for a sphere with a volume of 5π/3.

b. Evaluate this derivative when r = 2 and h = 1.