Answer is 12

Read Below:

To solve for the missing number, we need to identify the pattern in the given numbers. Looking at the numbers horizontally, we can see that the first and second numbers increase by 6 and 4 respectively to get to the next number. However, this pattern does not hold true for the last row as the difference between 16 and the missing number is not the same as the difference between 13 and 16.

Instead, we can look at the numbers diagonally to identify a different pattern. If we subtract 4 from 11, we get 7, which is the first number in the diagonal. If we subtract 4 from 15, we get 11, which is the second number in the diagonal. Following this pattern, we can subtract 4 from 16 to get the missing number:

5, 11, 15

13, 16, 12

Therefore, the missing number in the number matrix is 12. Here is a diagram to illustrate the pattern:

5 11 15

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13 16 ?