Find the slope if it exists, of the line containing the pair (3,4) and (3,-7)

So you've got a cartesian plane, right? There are two coordinates here. Plot the first one ((3.4)) first. the '3' is on the x axis and the '4' is on the y axis. Go 3 across until you get to 3. and then go 4 up. Put a dot there.
Next, also plot the second one. To do this, go to 3 on the x axis, and then go down until you get to -7 on the y axis. Plot your point with a dot. Then, join the dots up, and hopefully, it'll be a linear relationship! 

The slope formula is y1-y2/x1-x2.
First thing you have to find which cordinates will be y1 and x1. Then which cordinates will y2 and X2
I will do it so (3,4)=(x1,y1) and (3,-7)=(x2,y2)
Now plug the numbers into the formula and get:
(4--7)/(3-3)
4--7=4+7=11
3-3=0
Now you have 11/0 for slope. If a slope has a 0 in the denominator it is undefined. So this slope is undefined.