Use Compound Interest Monthly Formula:
A = P(1 + r/n)^nt
A = Future Amount
P = Initial Amount
r = Interest rate
n = monthly
= 12 months
t = 15
In this case:
P = 2500
r = 7.8%
n = 12 months
t = 15 years
7.8% = 7.8/100
= 0.078
2500(1 + 0.078/12)^12(15)
= 8024.54 —> Final Answer.