Suppose you roll two dice find the number of elements in the event space of rolling a sum of 10

The event space is the list of all the different ways
that two dice could come up with a sum of 10.

Here they are:

Cube-A  Cube-B
     6           4
     4           6
     5           5

That's all the ways there are to roll a 10. 
I am surprised.

These three combinations are all the elements
there are in that event space.

Agc and bgd are vertical angles