9/10b - 23/24 = 3/4b + 5/6
First, get all the letters on one side, and all the numbers on the other:
9/10b - 3/4b = 5/6 + 23/24
Then get common denominators:
18/20b - 15/20b = 20/24 + 23/24
Simplify:
3/20b = 43/24
Get the letter alone:
3/20b x 20/3 = 43/24 x 20/3
b = 860/72
Do your own simplifications, I'm tired.