I’m not sure how to “explain your math thinking”.

Answer:
Step-by-step explanation:
The math thinking refers to the process you did to solve the sum 9 + 7.
To solve this we could think the following process:
1. We complete the first number to 10.
2. The completion subtracted one unit from 7, so now it's 6.
3. Then we sum the ten and the six, it's easier to operate with tens.
Therefore, the answer is 16.
Remember that not everyone solve math problems and exercises the same way, because we all are different from each other.