The first step is to subtract 5 from both sides, that leaves you with 2/3b = 15 - b.
Next, you would add b to both sides to get rid of the b. This leaves you with 5/3b = 15
To get rid of the 5/3, you just multiply both sides by the reciprocal. This would be 3/5. This leaves you with b = 9
Hope this helps :)
