What does the given function ft really mean find the

Question

In 2007, U.S. consumption of renewable energy was 6.8 quadrillion BTU (or 6.8x10¹⁵ BTU) Since the 1960's consumption has been growing at a rate (in quadrillion BTU's per year) given by f'(t) = 0.004t + 0.062 where t is the years after 1960.

A. What does the given function f'(t) really mean?

B. Find the function f(t) and describe specifically what it means and represents.

C. Estimate the U.S. consumption of renewable energy in 2020.