To calculate the area for the upper (left) graph, we can use x = 1, 2, 3 and 4 to find the upper limit of each rectangle:
Since the x-interval of each rectangle is 1 unit, the area of each rectangle is given by its y-value, so we have:
Now, for the bottom (right) graph, the limits of the rectangles are x = 2, 3, 4 and 5.
So, let's find the value of f(5):
So the area is given by: