The directions of this problem is "Write an equation in slope intercept form for the line that satisfies the given conditions"

The equation of a line in slope-intercept form looks like the following: y = mx + b ,

where m is the slope of the line and b is the y-intercept.

Given any 2 points (x_{1}, y_{1}) and (x_{2}, y_{2}) on a line, the slope (m) = (y_{2}-y_{1})/(x_{2}-x_{1}).

Whenever the slope (m) is undefined it means that when you try to calculate the slope given any 2 points on the line you'll end up with a zero in the denominator, which is undefined. That is, with an undefined slope you end up with a vertical line, which has the equation "x=some number".

That is, m = (y_{2}-y_{1})/(x_{2}-x_{1}) = (y_{2}-y_{1})/0 = undefined. This implies that x_{2}=x_{1}. So x is the same for any value of y on the line, which is why the equation is "x=some number"
and the line is vertical.

So the equation of a line, in slope-intercept form, with an undefined slope (m=undefined) crossing through the point (-3, 5) is: x= -3 , which is a vertical line.