pls show your step thank you.
If you have never learned this before then I don't know why you are attempting the question. Here is a link. Read it: Pauls Online Notes : Differential Equations - Separable Equations
$\displaystyle y\sqrt{1 - 9x^2}\,dy = 3(1 - y^2)\,dx$
$\displaystyle \frac{y}{1 - y^2}\,dy = \frac{3}{\sqrt{1 - 9x^2}}\,dx$
$\displaystyle \int{\frac{y}{1 - y^2}\,dy} = \int{\frac{3}{\sqrt{1 - 9x^2}}\,dx}$
Do you see how we've separated the terms so all the y's are on one side and all the x's on the other? That's what's meant by a separable DE.
You should be able to go from here.
P.S. not undermining you Mr F - it's just the OP had no idea what was meant by separable.