Idon't understand how to answer questions 8, 10, 11, and 12. i have already answered all the other questions on the paper. the way that i solved the other questions doesn't work on these ones as the answer i get is negative.
p. s. file with questions is attached

8) The figure is a heptagon. This means the sum of the interior angles would be 180(7-2) = 5 * 180 = 900. Then this means you can say that the sum of all angles would equal 900.

(133 + 106 + 120 + 133 + (13 - 9)) + (m + m + m) = 900
Combine Like terms
496 + 3m = 900
Subtraction
3m = 404
Division
m = 404/3

If the answer doesn't seem right, just plug it in!

496 + 3(404/3) = 900
496 + 404 = 900
900 = 900

10) Same thing. The sum of the interior angles in a pentagon are 540. 

(122 + 90 + 88 + 96) + k = 540 
396 + k = 540
k = 144

11) The angle supplementary to the angle which measures 138 is 42. The sum of all the interior angles of a quadrilateral is 360. Let us call the missing INTERIOR angle x. 

(104 + 98 + 42) + x = 360
244 + x = 360
x = 116
So the missing EXTERIOR angle is 180 - 116 which is 64.

12 is a bit confusing without showing you sorry :(

He gained 60,900 dollars for that land