We know the length of this section is 3.5m. For the height/width, we can look at rectangle C. The height of C is 3.8m, and we see the part of C that is NOT part of B is 2m long. So we subtract 2 from 3.8 to find the height of B.
Took must make a 92 on the next test. (81+84+84+69+76+x)/6=81 (394+x)/6=81 Multiply by 6 on both sides 394 + x = 486 Subtract 394 from both sides. x= 92