The figure below shows the rate, $f(x)$, in thousands of algae per hour, at which a population of algae is growing, where $x$ is in hours.

(a)
Estimate the average value of the rate over the interval $x=-1$ to $x=1$.
average value = (thousands of algae/hr)

(b)
Estimate the total change in the population over the interval $x=-3$ to $x=3$.
total change = (thousands of algae).