Answer
Jan cannot cancel out the numerators and the denominators, for she is dividing fractions and not multiplying them. The correct way to simplify is below.
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:
$$ \frac{x}{3}\times \frac{x}{7}\\ \frac{x^2}{3\times \:7}\\ \frac{x^2}{21}$$
