Answer:
25
Step-by-step explanation:
The pattern is + 1, + 3, + 6,... i.e. + 1, + (1 + 2), + (1 + 2 + 3),...
.'. Missing number = 15 + (1 + 2 + 3 + 4) = 25.
it’s the 3rd one. so.. 5/8