If Bob works alone for one hour, he will get 1/6 of the yard work done. Working alone for two hours, Bob will get 2/6 = 1/3 of the yard work done. When Bob and Tom work together for two hours to finish the yard work, Bob will have done 1/3 of the work, which means Tom must have done 2/3 of the work in the two hours. Therefore if Tom works alone, the time he would take to finish the yard work is given by:
2/(2/3)=(you can calculate) hours
