Explanation

Complete series 6,9,13,16,20,23, 26,30

6+3=9

9+4=13

13+3=16

16+4=20

20+3=23

23+4=27

27 + 3=30

6+3=9 9+4=13 13+3=16 16+4=20 20+3=23 23+4=27 27±3=30

SH18-8-2-2023