Stefan’s Law states that a body emit radiant energy to a sink at absolute zero

Question

according to the formula R = kT4, where R is the measure of the rate of emission of
the rate of energy per square unit of area, T is the measure of the Kelvin temperature
of the surface and k is a constant.
a. Find the average rate of change of R with respect to T as T increases from 200 to
300.
b. The instantaneous rate of change of R with respect to T when T is 200.

Answer 1

I assume you mean R(T) = kT^4
(a) as always, this would be
(R(300)-R(200))/(300-200) = 65*10^6 k

(b) dR/dT = 4kT^3 = 16*10^8 k