please help, i'm not sure if i'm on the right track.

**A spherical hailstone grows in a cloud. The hailstone maintains a spherical shape while its radius increases at a rate of 0.2 mm/min. ** **a) Express the radius, r, in millimeters, of the hailstone, as a function of the time, t, in minutes.** *i came up with the answer, * *r(t) = 0.2t* *but i'm not sure if its right* correct **b) Express the volume, V, in cubic millimeters, of the hailstone, in terms of r.** *i got,* *V(r) = * you went one step too fast ... **c) Determine (Vor)(t)** *Vor(t) = * *not sure if thats right either?* correct **d) What is the volume of the hailstone 1 h after it begins to form?**

... sub in 60 for t and calculate the volume.