Equivalent Fractions · Superchallenge problem

The fraction $\dfrac{12}{21}$ is equivalent to $\dfrac{4}{7}$, and its denominator is its numerator with the digits reversed. How many fractions equivalent to $\dfrac{4}{7}$ (counting $\dfrac{12}{21}$) have a two-digit numerator and a denominator that is that numerator with its digits reversed?