You can put this solution on YOUR website! There are two ways to do this...
1) If two points have the same y cordinate, then it is a horizontal line and the slope is zero.
2) You can also find the slope by using the following equation
m(the slope) = Y2 - Y1 dvided by X2 - X1
-2 - (-2) / -10 - 3 = 0 / -13 = 0
so m = 0
Hope this helps