Question

Can someone help me with this question please.

Answer 1

The answer would most defiantly be “21”, choice c “21”

Answer 2

21

Explanation:

The formula for triangular numbers is n×(n+1)÷2 (n is the step of next number)

we have 1, 3, 6, 10, 15 so the next step would be 6th

6×(6+1)÷2 = 21