PLEASE I NEED HELP ASAP

Armando found the volume of the figure below by using the steps shown.
A rectangular prism with a length of 18 inches, width of 5 inches, and height of 8 inches. A triangular prism with a base of 18 inches and height of 6 inches. The prism has a height of 5 inches.

Total Volume = Volume of rectangular prism + volume of triangular prism = 5 (8) (18) + one-half (6) (18) (8) = 720 + 432 = 1,152 cubic inches.

What mistake, if any, did Armando make?
Armando determined the volume correctly.
Armando used the wrong formula for the total volume.
Armando used the wrong dimensions for the triangular prism.
Armando did not apply the order of operations correctly.