Not sure if you've learned this but we can use exponents to make an equation.
y = cn^x
with y being the new price, c being the original, n being the rate of increase (or decrease) and x being years. This use of exponents has many names in economics and calculus but i wont bore you with that.
in our case:
we can find n by finding how much will be left of the price.
1.00 - 0.25 = 0.75
f(x) = (22500)(0.75)^x
f(5) = (22500)(0.75)^5
=$5339.35
