Find the missing number?

Step 1:
Start From The top row left element and reach to the right element. Add 8 to get second number then subtract 3 to get third number.

Step 2:
Down from right element to Right element of the second row and reach to the left element. Add 8 to get second number then subtract 3 to get third number.

Step 3: Down to the Left row element of the third row and reach to the Right element. Add 8 to get second number then subtract 3 to get third number.

Thus,
Missing Number = 29 - 3 = 26.