What you are asking is called the left Reimann sum since we are using the left endpoints of each interval.
The values of Δxk are (2-0), (5-2) and (8-5). That is, 2, 3 and 3.
The values of ck are 0, 2 and 5
The values of f(ck) are (02-1), (22-1) and (52-1). That is, -1, 3 and 24.
So, each term in the Reimann sum is f(ck)Δxk and they are (-1×2), (3×3) and (24×3)
These values are -2, 9 and 72.
So, adding them together, the Reimann sum is 79.