Test statistic for a partial correlation

A batch of $19$ students is examined in three subjects—Statistics $(x_1)$, Mathematics $(x_2)$ and Computer Programming $(x_3)$. It has been given that $r_{13.2}=0.6$. It is expected that $x_2$ will affect the correlation between $x_1$ and $x_3$ (i.e., the partial correlation between $x_1$ and $x_3$ after eliminating the effect of $x_2$ is zero). The value of test statistic for testing $H_0:\rho_{13.2}=0$ against $H_1:\rho_{13.2}\ne0$ is: