We will assume the we are talking about simple interest.

r = interest rate

t = 6 years the period of time

P = $2,500

A = $3,325

A = P(1 + rt)

r = (A - P)/(Pt)

r = (3,325 - 2,500)/(2,500*6)

r = 0.055 

Now we will find A, the future value,  for P = $7,500, interest rate r = 0.055 or 5.5% and time period t = 6 years:

A = P(1 + rt)

A = 7,500(1 + 0.055*6)

A = $9,975

The final value of a deposit of $7,500 at the same interest rate for the same period of time is $9,975.