A physicist is monitoring the amount of energy being generated by a solar panel. The function $E(h)$ gives the amount
of energy generated, in Joules, at time $h$ in hours. After 3 hours, she notes that $E(3) = 920$ and $E'(3) = 220$.
1. What are the units of $E'(h)$?
2. Give a physical interpretation of $E'(3) = 220$, by writing a sentence that describes it in context and without
using the word rate.
3. Give an estimate of $E(2)$.
4. [Reach] Approximately how much energy will the solar panel have generated after 8 hours?