請大家幫幫忙　數學難題!!!

i) C = hr^2 + kr^3 (h,k = non-zero number)
when r=4 , C=96
96 = 16h + 64k
6 = h + 4k --------(1)
when r=1 , C=3
3 = h + k --------(2)
(1) - (2)
3 = 3k
k = 1
put k = 1 into (2) , h = 2
The equation connecting C and r is C = 2r^2 + r^3 .

ii)when r = 2
C = 2(2^2) + 2^3
C = 8 + 8
C = 16
The cost of mmaking a metallic sphere of radius 2 cm is $16 .