Answer:
10
Explanation:
4+5+6=15,
4+5+7=16,
4+5+8=17,
4+5+9=18,
4+6+7=17,
4+6+8=18,
4+6+9=19,
4+7+8=19,
4+7+9=20,
4+8+9=21,
5+6+7=18,
5+6+8=19,
5+6+9=20,
5+7+8=20,
5+7+9=21,
5+8+9=22,
6+7+8=21,
6+7+9=22,
6+8+9=23,
7+8+9=24.
There are sums 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 10 different sums in total.