### Addition of fractions with different but related denominators

To add fractions with different denominators, we must first convert them to equivalent fractions with the same denominators.

\begin{align}\frac{3}{6} + \frac{3}{4} &= \frac{6}{12} + \frac{9}{12} \text{(convert each to equivalent fractions with same denominators)} \\&= \frac{15}{12} \\&= 1\frac{3}{12} \text{(convert the improper fraction to a mixed number)} \\&= 1\frac{1}{4} \text{(simplify)}\end{align}