The answer is 21. I found it out by doing this...I found out that the triangle is 6,the circle is 4,the square is 8,and the hexagon is 7.I frist thought that the square was 10 for the first row but going down would not allow it so I changed it to 8 so that it would fit all of the other numbers and I kept trying other numbers for other shapes until I found my answer of 21.
Method 1 Yes it would work. If he kept adding 1 to the circle he would get the correct answer of 21.
Method 2 Yes it would work.If you divide 16 and 2 you would get 8 and the square is 8.Then subtract 14 and 8 to get six and that is the number of the triangle.
Method 3 Yes it could work.If triangle=6 and square=8 and 6+2=8.