Exponential decay problem

After how many years will $100 invested at an annual rate of 6% compounded continuously be worth at least 450$? (Use the formula An=A0e^rt)

Your problem is one of "growth" , not decay

100(e^.06t = 450
e^.06t =4.5
.06t lne = ln 4.5
.06t = ln 4.5
t = ln 4.5 / .06 = 25.068 years