159686

The answer is 21

Triangles are 6, squares are 8, hexagons are 7 and circles are 4.

First I worked out squares (because there were 3 of them in a column). They must be less than 10, I tried out 8, then cross-referenced with the top line-if 8 was correct, then triangles on top line must be 6. I knew that if triangles were 6, then the circles could be 4, I then tried out 4 for all the circles (along with the other test numbers) and this worked, making hexagons 7.