This exercise is asking you to find the value of b or solve for b, to do so you have to isolate or leave b alone by doing different mathematical operations according to the given equation.
The given equation is 12b+b-4b+3=12, which is a three step equation meaning that in order to solve for b you have to perform three different mathematical operations, in this case combining of like terms, subtraction, and division.
12b+b-4b+3=12 Combine like terms
9b+3=12 Subtract 3 in both sides
9b=9 Divide by 9 in both sides to isolate b
b=1
The value of ''b'' by which this equation is true is 1.