explanation plz :( i need help with this task

$\frac{11}{12}+\frac{10}{11} = \frac{11 \cdot 11}{12 \cdot 11}+\frac{10 \cdot 12}{11 \cdot 12} = \frac{121}{132} + \frac{120}{132} = \frac{241}{132}$

The trick is to expand the fractions, so the denominator is the same for each fraction.