Question

At time t = 0, a seed is planted. After t weeks, the height of the plant is given by f(t) = 0.3t² = 0.6t = 0.5 inches. At what rate is the plant growing after

Answer 1

incomplete posting, and you probably meant + instead of =
but ....

f ' (t) = .6t^2 + .6

whatever is given for t, sub it into the last expression

Answer 2

Actually it would be:
f ' (t) = 0.6t + 0.6
(not t squared as the original reply showed)