Problem 305

The equation $a(x+2)+b(x+2)=60$ has a common factor of $x+2$ on the left side. Thus, we can re-write the equation as $(a+b)(x+2)=60$. When $a+b=12$, we obtain $12 \cdot(x+2)=60$ and so $x+2=5$ which gives $x=3$.