#### Answer

$(\sqrt{y}-3x)^{2}=9x^{2}-6x\sqrt{y}+y$

#### Work Step by Step

$(\sqrt{y}-3x)^{2}$
Evaluate this power using the formula for squaring a binomial. The formula is $(a-b)^{2}=a^{2}-2ab+b^{2}$. In this expression, $a=\sqrt{y}$ and $b=3x$
Substitute the known values in the formula and simplify:
$(\sqrt{y}-3x)^{2}=(\sqrt{y})^{2}-2(3x)\sqrt{y}+(3x)^{2}=...$
$...=y-6x\sqrt{y}+9x^{2}=9x^{2}-6x\sqrt{y}+y$