Question 593172
A is the amount after some time t ($200000 and 18 yr in your case)


P is the principal (initial investment that you're trying to find)


r is the rate of interest ___ this particular formula assumes continuous compounding


e is Euler's Number, the base for natural logarithms ___ there is a key for it on scientific calculators
___ there is a calculator in Windows ___ when you open it, click on view to select scientific


200000 = P e^(.04 * 18)


200000 / [e^(.76)] = P


93533.29 = P (approx)