To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $4c$ and $2b$ is $4bc$. Multiply $\frac{3b}{4c}$ times $\frac{b}{b}$. Multiply $\frac{c}{2b}$ times $\frac{2c}{2c}$.
$$\frac{3bb}{4bc}+\frac{c\times 2c}{4bc}$$
Since $\frac{3bb}{4bc}$ and $\frac{c\times 2c}{4bc}$ have the same denominator, add them by adding their numerators.
