Quantitative reasoning question

The example shows an input of '9' connected to a diamond containing '3', which results in an output of '5' in the circle.
Let $I$ be the input number(s), $D$ be the number in the diamond, and $O$ be the output number in the circle.
For the example: $I = 9$, $D = 3$, $O = 5$.
We test the relationship $O = I - D - 1$:

This pattern holds true for the example.

For , there are two input numbers, '6' and '7', connected to the diamond. The number inside the diamond is '5'. The output is '?'.
When multiple numbers are inputs to a single operation in such puzzles, they are typically combined by addition.
So, the combined input $I$ for is the sum of '6' and '7'.
The number inside the diamond $D = 5$.
The output $O = ?$.

Substitute $I = 13$ and $D = 5$ into the pattern $O = I - D - 1$:

The missing number is 7.

The final answer is 7.