Answer:
0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78
Explanation:
It looks like everytime there is a new number, you add it +1 everytime. Let me explain. 0 + 1 is adding 1. Then, when you get to 3, you went from 1 to 3. When you got to 6, you went from 3 to 6. So, the pattern is +1, then +2, then +3, and so on.
See in the answer, I am going up +1 everytime.