Geometric Gradient Series Factors Example 2: Engineers at seaWorld modified an existing boat. The modifications costs $8000 and it is expected to last 6 years with a salvage value $1300. The maintenance cost is expected to be $1700 the first year and increasing by 11% per year thereafter. Determine the equivalent present worth at 8% annual interest rate. Unknown interest Rate Example: John can make investment of $3000 now in order to receive $5000 five years from now. - Determine the rate of return - If John can receive 7% per year on a certificate of deposite, which investment should he make?