To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $3$ and $4$ is $12$. Multiply $\frac{a+3}{3}$ times $\frac{4}{4}$. Multiply $\frac{a-3}{4}$ times $\frac{3}{3}$.
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $3$ and $4$ is $12$. Multiply $\frac{a+3}{3}$ times $\frac{4}{4}$. Multiply $\frac{a-3}{4}$ times $\frac{3}{3}$.
