Answer:
335,979 people (in Year 2020)
Explanation:
Initial Population (Year 2010) = 250,000
Rate of Growth = 3% = 3/100 = 0.03
We want the population of the town in Year 2020 (at this rate). That is 10 years from now.
The formula for compound growth is:

Where
F is the future value (in year 2020)
P is the present value (250,000)
r is the rate of increase per year (0.03)
t is the time in years (t = 10)
Lets substitute and find the value:

Rounded, that would be:
335,979 people (in Year 2020)