Verified answer

Well, the instantaneous rate of change is at a single point, so it doesn't really make sense to ask for the instantaneous rate of change on an interval. (it's called instantaneous because you're only computing for a single instant)

However, f(t) = t^2 - 3 => f'(t) = 2t.

So for any point t in [2,2.1], 2t gives the instantaneous rate of change.

Recall that for f(x) = ax^b, where a and b are real, f'(x) = abx^(b-1).