Solve the problem.
The profit made when t units are sold, t>, is given by P²-36t+320. Determine the number of units to be sold in order for P>0 (a profit is made).
The future value of $6000 invested for 5 years at rate r, compounded annually, is given by S=6000(1+r)^5. Find the rate r, as a percent that gives a future value of $8415.31. Round to the nearest whole percent.