1/12+7/9=63/72

1/12+7/9=63/72 ?

$\begin{array}{rcl} \frac{1}{12} + \frac{7}{9}\\ &=& \frac{1}{12}\cdot\frac{3}{3} + \frac{7}{9}\cdot\frac{4}{4}\\ &=& \frac{3}{36} + \frac{28}{36}\\ &=& \frac{31}{36}\cdot\frac{2}{2}\\ &=& \frac{62}{72}\\ \end{array}$