159555

I found out that a square is two more then a triangle. Then I worked it out from there that a square must be 8 and a triangle must be 6. I then worked out a circle was 4 because there was a gap of 8, and there were two circles in the line. Finally, I looked at the value of a hexagon. I worked out that I needed 14 more to make the line with 2 hexagons and 2 squares. I knew that the 2 squares made 16 so that left 14 for the 2 hexagons. I split 14 and it made 7.
The final line was 7+6+4+4= 21