At Mauna Loa, Hawaii, atmospheric carbon dioxide levels in parts per million (ppm) have been measured regularly since 1958. The function defined by L(t) = 0.022t² + 0.55t + 316 + 3.5 sin(2πt) can be used to model these levels, where t is in years and t = 0 corresponds to 1960.

(a) Graph L(t) on [0, 30].
(b) Find L(25), L135.52, and L(50.2).
(c) Find L′(50.2) and interpret.