Answer:
20.4 years
Explanation:
The nper formula in excel comes handy in this scenario:
=nper(rate,pmt,-pv,fv)
Rate is the monthly rate of 5.4%/12
Assuming actual investment is $5,000 which is pv
The triple amount would be $5,000*3=$15,000 which is future value fv.
pmt is the regular cash flow the investment which is zero
=nper(5.4%/12,0,-5000,15000)= 244.68 months
Yearly it can be expressed as = 244.68/12 =20.39 years
When rounded to one decimal place it becomes 20.4 years