After knee surgery, your trainer tells you to return to your jogging program slowly.  He suggests jogging for 12 minutes each day for the first week.  Each week thereafter, he suggests that you increase that time by 6 minutes per day.  How many weeks will it be before you are up to jogging 60 minutes per day?


Adding 6 minutes to the weekly jogging time for each week creates the sequence:  12, 18, 24, ...

an= a1+(n-1)d
an= 60=12 +(n-1)6
n= 9 weeks