Answer: There will be 313600 population on beth's 16 birthday.
Step-by-step explanation:
Since we have given that
When Beth was born , the population of her has increased = 850 per year
Let the initial population be x
and let the number of year be n
So, our linear equation becomes,

On her 9th birthday,
The population becomes 307,650.
So, it becomes,

So, initial population becomes 300000.
Now, on 16th birthday,

So, there will be 313600 population on beth's 16 birthday.