To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $2x^{2}$ and $8x$ is $8x^{2}$. Multiply $\frac{5}{2x^{2}}$ times $\frac{4}{4}$. Multiply $\frac{3}{8x}$ times $\frac{x}{x}$.
Since $\frac{5\times 4}{8x^{2}}$ and $\frac{3x}{8x^{2}}$ have the same denominator, add them by adding their numerators.
$$\frac{5\times 4+3x}{8x^{2}}-\frac{1}{4}$$
Do the multiplications in $5\times 4+3x$.
$$\frac{20+3x}{8x^{2}}-\frac{1}{4}$$
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $8x^{2}$ and $4$ is $8x^{2}$. Multiply $\frac{1}{4}$ times $\frac{2x^{2}}{2x^{2}}$.
$$\frac{20+3x}{8x^{2}}-\frac{2x^{2}}{8x^{2}}$$
Since $\frac{20+3x}{8x^{2}}$ and $\frac{2x^{2}}{8x^{2}}$ have the same denominator, subtract them by subtracting their numerators.
