Answer
$$\frac{x^2}{20}$$
Work Step by Step
Recall, one never divides by a fraction. Rather, if we want to divide by a fraction, we multiply by the reciprocal of the fraction. Recall, the reciprocal of a fraction is that fraction with the numerator and the denominator switched. Thus, we find:
$$\frac{x}{4}\div \frac{5}{x}\\ \frac{x}{4}\times \frac{x}{5} \\ \frac{x^2}{4\times \:5} \\ \frac{x^2}{20}$$
