The slope of a point is

so


having the slope equal zero just means that there is no change in the y values
which means that they are on the same horizontal line which they are at y=7
F,e and h,i are vertical angles i think.
You did not attach anything to go with it, but the independent variables are always the x values, and the dependant variables are always the y value. To find to slope do rise/run.<span />
Simplify the expression —48
Hope it helps :)