8. To the right is a graph of the cost curves for some firm. Total Cost for this firm if it produces 20 units of output is:

   Remember that Total Cost at any level of output is just ATC (Average Total Cost) multiplied by Q (output). When this firm produces 20 units of output ATC is 15 (the height of the ATC curve at 20.) So, Total Cost is equal to the shaded area to the right which is 15 x 20 = 300.