I don't understand how this equation works can someone please help

The area of a region under a curve is greater than the area of an inscribed rectangle and less than the area of a circumscribed rectangle. Intuitively, we understand that somewhere between the inscribed and circumscribed rectangles there is a rectangle whose area is precisely equal to the area of the region under the curve:

a^b f(x) dx = f (c) (ba)

The average value of a function on the interval[a;b]

is determined by Average value=1/ba a^b f(x) dx

The efficiencye (in % ) of an automobile engine is given bye=0.768s0.00004s3

, wheresis the speed (in km/h) of the car. Find the average efficiency with respect to the speed fors=32km/h tos=89km/h. Round the answer to one decimal place.