First get like things on the same side:
-5/6b - 1/2b= -2/3 - 3/4
Then find equivalent fractions to make the equation easier to solve.
-5/6b - 3/6b= -8/12 - 9/12
Then just add things together and solve.
-8/6b= -17/12
-8b= 6(-17/12)
-8b= -17/2
b= (-17/2)/-8
b= 17/16
You can then plug the answer back into the original question to make sure it is the correct answer.
If you look carefully at the grid, you will see that each increment is by 1/8.
That means that for the x-coordinate of P, you can count from -4/8 to get -5/8.
For the y-coordinate, you can count up from 0 to get 3/8.
Then, the answer is (-5/8, 3/8), or the third answer.
You would do 20 • 3=60 and the you would add 20 • 1/5=4 so, your total is 64in.