Answer :
[tex]\begin{gathered} b-7=12 \\ An\text{ equation is an expression where everything on the right side of the } \\ \text{equality sign equals everything on the left side. This means that} \\ \text{whatever you add or subtract from the left, you must do the same} \\ t\text{o the right.} \\ b-7=12 \\ \text{Add 7 to both sides to eliminate the -7 on the left side} \\ b-7+7=12+7 \\ b=19 \end{gathered}[/tex]