Bruce and Robbie each open up new bank accounts at time 0. Bruce deposits 200 into his bank account, and Robbie deposits 50 into his. Each account earns the same annual effective interest rate. The amount of interest earned in Bruce's account during the 10th year is equal to X: The amount of interest earned in Robbie's account during the 15th year is also equal to X. Find the effective rate of discount and the discount factor.