The original population is 2500
The decreasing rate is 3.5%/year
You have to write the expression for the exponential decay and calculate the population of the town after 5 years.
An exponential decay can be calculated as:

Where
a is the initial value
r is the decay rate → expressed as a decimal value
x is the time that have passed
Express that rate as a decimal value:
r=3.5/100=0.035
The exponential decay for this population can be expressed as:

For x=5 years the population (y) will be:

After 5 years the population will be 2093