There are $106$ people sitting in a row facing North. The position of A from the right end is $16\text{th}$. How many people are sitting to the left of A in the row?

Total number of people in the row = $106$.
Position of A from the right end = $16\text{th}$.

The number of people sitting to the left of A is simply the total number of people minus A's rank from the right end:

$$\text{People to the left of A}=\text{Total}-\text{Rank from Right}$$

$$\text{People to the left of A}=106-16=90$$

Thus, there are $90$ people sitting to the left of A.