Answer:
the pattern step number of second step is added to number of balls used of first step to get number of balls used of second step
that is
1 + 2 ( number of balls added to pattern step number) = 3 (number of balls used)
in the same way
6 + 4 = 10 ( first blank )
5 + 10= 15 ( second blank)
15 + 7 = 22 ( third blank )
22 + 8 = 30 ( fourth blank)
