Michelle can fold 4/54 baskets per minute = 8/108 baskets per minute.
Ruby can fold 4/108 baskets per minute.
Each minute Michelle and Ruby work together, they can fold
8/108 +4/108 = 12/108 = 1/9
of a basket of clothes. For 8 baskets of clothes, it will take them
(8 baskets)/(1/9 baskets/minute) = 72 minutes
