(Please show me how you solved this!!)

The rate r(t) at which forest is burned in a forest fire, t hours is given in the tabs after the start of the fire.
t(hours) 0 3 6 9,
r(t) (acres/hour) 5 9 14 16.
The amount of forest burned in the first nine hours has:
(A) a lower estimate of 28 acres and an upper estimate of 39 acres.
(B) a lower estimate of 14 acres and an upper estimate of 23 acres.
(C) a lower estimate of 70 acres and an upper estimate of 115 acres.
(D) a lower estimate of 115 acres and an upper estimate of 150 acres.
(E) a lower estimate of 84 acres and an upper estimate of 117 acres.

since the chart shows the rate of burn, the amount burned is the area under the graph. Since the curve is concave down, using left-side rectangles will over-estimate the area. That is, using 3 intervals of width 3,

3(f(0)+f(3)+f(6))
The right-side estimate is an under-estimate: 3(f(3)+f(6)+f(9))

Better review Riemann sums.