There are 10soccer teams in the s-league. each team plays one match against each of the other teams. how many matches will be played in the league altogether?

1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 are your team numbers
1 - 2
1 - 3
1 - 4
1 - 5
1 - 6
1 - 7
1 - 8
1 - 9 
1 - 10
2 - 3
2 - 4
2 - 5
2 - 6
2 - 7
2 - 8
2 - 9
2 - 10
3 - 4
3 - 5
3 - 6
3 - 7
3 - 8
3 - 9
3 - 10
4 - 5
4 - 6
4 - 7
4 - 8
4 - 9
4 - 10
5 - 6
5 - 7
5 - 8
5 - 9
5 - 10
6 - 7
6 - 8
6 - 9
6 - 10
7 - 8
7 - 9
7 - 10
8 - 9
8 - 10
9 - 10

45 matches in all >.< :)

The correct answer will be d. -4