Answer:
a = 4
Step-by-step explanation:
The function y = f(x) = 5 is simply a horizontal straight line
the interval x=a and x= 8 represent vertical straight lines that intersect x = a and x = 8.
Hence the area above the x-axis that is bound by f(x) on the top and x=a & x=8 on the sides is simply a rectangle with height = 5 and length = ( 8 - a ), and its area is given by
area = height x length = 5 (8-a)
we are given that the area = 20,
hence
area = 20 = 5(8-a)
(8-a) = 20/5
8-a = 4
-a = 4 - 8
-a = -4
a = 4
