A second method...
Slope of far right line is -12/10 it will intersect the y axis at 14.4
then the area formed by this largest triangle is
1/2 ( 14.4 x 12) then subtract the little we-just-added triangle
- 1/2 (2.4 x 2) and the little triangle in the diagram
-1/2 (2 x (12-p)) and the medium sized triangle in the lower left
-1/2 (p x 12) and what is left = 27 (given)
86.4 - 2.4 - 12 + p - 6p = 27
72 - 5p = 27
-5p = -45
p = 9