Sophie found the volume of the figure below by using the steps shown. A rectangular prism with a length of 28 millimeters, width of 21 millimeters, and height of 4 millimeters. A rectangular pyramid with a base of 28 millimeters by 21 millimeters and height of 26 millimeters.

Total Volume = B h + one-third B h = 4 (21) (28) + one-third (21) (28) (30) = 2,352 + 5,880 = 8,232 cubic millimeters.

What mistake, if any, did Sophie make?
Sophie determined the volume correctly.
Sophie used the wrong formula for the total volume.
Sophie used the wrong height for the pyramid.
Sophie did not apply the order of operatio