Answer
$y=-3x-1.$
Work Step by Step
If two lines are parallel then their slopes must be equal.
We know that if the slope of a line is $m$ and it contains $P_1(x_1,y_1)$, then its equation is: $y-y_1=m(x-x_1).$ It is parallel to $y=-3x$, hence its slope is $m=-3$. Hence here: $y-2=-3(x-(-1))\\y-2=-3x-3\\y=-3x-1.$
