The equation of a line in slope intercept form is given as ;
y= mx + c where m is the gradient and c is the y intercept
The point given is { -3,0}
The line is parallel to line x=0 , this mean it is the y-axis and it is a vertical line
So if the line is vertical and passes through point {-3, 0} then it means the equation for the line will be;
x = -3
so if y=0 when x =-3 then from the general form of
y= mx + c
0 = 0 * {-3 } + c
0 = 0 + c ------c= 0 , to mean y-intercept is 0 thus;
the equation will remain as;
x = -3