ΠDraw a sketch to help you see this.
The radius of the cup at the top is 3/2.
The water forms a triangle similar to the cone so the radius of the water, r is to the height of the water h as 3/2 is to 5, i.e. r = 3h/10
The volume of water when it is h high is V = Πr2h = Π(3h/10)2h =( 9Π/100)h3
Differentiate: dV = (9Π/100) * 3h2 dh
dV= .5, h = 5/2
.5 = (27Π/100) * (25/4) dh = 27Π/4 dh
dh = (2/27Π) = .023579 in/sec