How much money has to be invested at 2.3% interest compounded continuously to have $41,000 after 17 years?

I'd suggest you look up the "continuous compounding formula."  It is 

A = Pe^(rt), where A is the accumulation after t years, P is the original amount (Principal), r is the annual interest rate as a decimal fraction, and t is the elapsed time in years.

Here, A = $41000 = P e^(0.023*17).  How would you go about solving this for P?  That's your job here.

    $41000
= P = ??
e^(0.023*17)

Hint:  calculate 0.023*17 first, and then use your result as the exponent of the base "e."