The common factor is b since it is divisible by both 2b and 5b
Answer:
The top graph on the right that is shaped like an M. :)

Let's solve ~

![\qquad \sf \dashrightarrow \:[( 8 \sdot3) + (8 \sdot2i) + (5i \sdot3) + (5i \sdot2i)] -[( 4 \sdot4) + (4 \sdot - i) + (i \sdot4) + (i \sdot - i)]](https://tex.z-dn.net/?f=%5Cqquad%20%5Csf%20%20%5Cdashrightarrow%20%5C%3A%5B%28%208%20%5Csdot3%29%20%2B%20%288%20%5Csdot2i%29%20%2B%20%285i%20%5Csdot3%29%20%2B%20%285i%20%5Csdot2i%29%5D%20-%5B%28%204%20%5Csdot4%29%20%2B%20%284%20%5Csdot%20-%20i%29%20%2B%20%28i%20%5Csdot4%29%20%2B%20%28i%20%5Csdot%20-%20i%29%5D)
![\qquad \sf \dashrightarrow \:[24+ 16i + 15i+ 10i {}^{2} ] -[16 - 4 i+ 4i - i {}^{2} ]](https://tex.z-dn.net/?f=%5Cqquad%20%5Csf%20%20%5Cdashrightarrow%20%5C%3A%5B24%2B%2016i%20%2B%2015i%2B%2010i%20%7B%7D%5E%7B2%7D%20%5D%20-%5B16%20-%204%20i%2B%204i%20-%20i%20%7B%7D%5E%7B2%7D%20%5D)
![\qquad \sf \dashrightarrow \:[24+ 31i+ 10 {}{( - 1)} ] -[16 - ( - 1){}^{} ]](https://tex.z-dn.net/?f=%5Cqquad%20%5Csf%20%20%5Cdashrightarrow%20%5C%3A%5B24%2B%2031i%2B%2010%20%7B%7D%7B%28%20-%201%29%7D%20%5D%20-%5B16%20-%20%28%20-%201%29%7B%7D%5E%7B%7D%20%5D)
![\qquad \sf \dashrightarrow \:[24+ 31i - 10 {}{} ] -[16 + 1{}^{} ]](https://tex.z-dn.net/?f=%5Cqquad%20%5Csf%20%20%5Cdashrightarrow%20%5C%3A%5B24%2B%2031i%20-%2010%20%7B%7D%7B%7D%20%5D%20-%5B16%20%20%2B%201%7B%7D%5E%7B%7D%20%5D)
![\qquad \sf \dashrightarrow \:[14+ 31i {}{} ] -[17{}^{} ]](https://tex.z-dn.net/?f=%5Cqquad%20%5Csf%20%20%5Cdashrightarrow%20%5C%3A%5B14%2B%2031i%20%7B%7D%7B%7D%20%5D%20-%5B17%7B%7D%5E%7B%7D%20%5D)

I hope you understood the procedure ~
Step-by-step explanation:
phukan = x
Nanwan = y
let this be a simultaneous equation.
x - y = 18.... equation i
x + y = 100.... equation ii
subtract equation i from equation ii
= 2y = 118
y = 59
substitute y = 59 in equation ii to get x
x + 59 = 100
x = 100- 59
x = 41
Nanwan = 59, Phukan = 41
Well you would do 1/2bh, 11 x 3 is 33 so half of that is 16.5