Answer:
15 dots
Step-by-step explanation:
formula :: 1/2 x n ( n +1 )
fig 1 ; 1 /2 x 1 ( 1+1 ) = 1 dot
fig 2 :; 1/2 x 2 ( 2+1 ) = 3 dots
......
fig 5 :: 1/2 x 5 ( 5+1 ) = 15 dots
