do not know how to get d

May 2001 #12 Bruce and Robbie each open up new bank accounts at time 0. Bruce deposits 100 into his bank account, and Robbie deposits 50 into his. Each account eams an annual effective discount rate of d. The amount of interest eamed in Bruce's account during the 11th year is equal to X. The amount of interest earned in Robbie's account during the 17 year is also equal to X. Calculate X