I'm having a really difficult time trying to solve these problems. Could someone please explain them to me?

1. The total annual enrollment (in millions) in U.S. elementary schools for the years 1975-1996 is given by the model

$\displaystyle E = -0.058x^2 - 1.162x + 50.604$

Where x=0 corresponds to 1975, x=1 corresponds to 1976, and so on. For this period, when was ennrollment the lowest? To the nearest tenth of a million, what was the enrollment?

2. A parabolic arch has an equation of $\displaystyle x^2 + 20y - 400 = 0$, where x is measured in feet. Find the maximum height of the arch.

Thanks in advance.