Likelihood ratio test of two sample normal distributed with known means(which is 0) and unknown variance

Question

Let $X_1,X_2,\cdots ,X_n$ be random sample form $N~(0,\theta_1)$ and Let $Y_1,Y_2,\cdots ,Y_m$ be random sample form $N~(0,\theta_2)$. Determine the $\lambda$, the likelihood ratio test in testing $H_0 : \theta_1=\theta_2$ and $H_1 : \theta_1 \neq \theta_2$. What F statistic is used in this test?