I have a practice problem that has me utterly confused.

I am suppose to find the present value of a continuous stream of income over 5 years if the rate of income is $\displaystyle 80e^{-.08t} $ and the interest rate is 10%.

I suspect the problem should be set up this way:

$\displaystyle

\int\ 80e^{-.08t} e^{-.10t} dt

$

but I cannot figure out how integrate this. Am I setting up the problem wrong?