To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $94$ and $188$ is $188$. Multiply $\frac{37a}{94}$ times $\frac{2}{2}$.
$$\frac{2\times 37a}{188}-\frac{3}{188}$$
Since $\frac{2\times 37a}{188}$ and $\frac{3}{188}$ have the same denominator, subtract them by subtracting their numerators.
