Answer: 3

We have explained the solution below.

Each number in the top row is a result of subtracting two numbers below it.

6 – 2 = 4 (in the top box)

19 – 10 = 9 (third row, first box)

7 – 6 = 1 (third row, last box)

Similarly, if we subtract 7 from 10 in the fourth row, we shall get 3.

To verify our answer, we check if 3 satisfies our equation for the above rows.

We shall subtract 3 from 9 in the third row, we get 6 (as in the second row). Now, we shall subtract 1 from 3 and we get 2 (as in the second row).

Hence, the missing number here 3 is correct.

Answer: 13

Include all the triangles as displayed in the picture.

There is ONE big triangle.

The big triangle consists of FOUR triangles.

Each two triangles (forming a diamond shape together) are further divided into FOUR smaller triangles.

We shall apply => 1 + 4 + (2 x 4) = 13

Answer: 8

2 + 6 + 9 = 17

6 + 3 + 8 = 17

7 + 7 + 3 = 17

So far, we understood that the sum of all equations on both LHS and RHS should be 17.

Hence,

5 + ? + 4 = 17

x + 9 = 17

x = 17 – 9 = 8