Answer:
63mm
Explanation:
7mm+8mm=15.
15×15=225
12×12=144(area equals base times height) add 225-144=81(here we are using the Pythagoras theory) so you search for the square root of 81 which is 9 meaning the height is 9. since we say area is 1/2base times height we should take 1/2 ×9×12=63.if the answer doesn't match with the answer in your book please tell me right away so that I can try another method thank you