Answer
$$ \frac{3}{7x}$$
Work Step by Step
We first put this in fractional form:
$$ \frac{7}{3} \cdot x \\ \frac{7x}{3} $$
Recall, the reciprocal of a fraction is that fraction with the numerator and the denominator switched. Thus, we find:
$$ \frac{3}{7x}$$