Question 153002
The formula for the slope using two points is,
{{{m=(y[2]-y[1])/(x[2]-x[1])}}}
Substituting with the two points,(-1,-3) and (-1,7) 

{{{m=(7-(-3))/(-1-(-1))}}}
{{{m=10/0}}}
The slope is undefined. 
It is a vertical line.
{{{drawing( 300, 300, -5, 2, -4, 10,grid( 1 ),circle( -1, -3, .2 ),circle(-1,7,.2),green(line( -1, -3, -1, 7
)))}}}