Every 3 minutes he decorates 5 cupcakes
he needs 60 cupcakes
60 cupcakes / (5 cupcakes / 3 min) = 36 minutes
He needs 36 minutes from the time he starts actual decorating
at 1:05 he has decorated 5 cakes....so he started decorating at 1:02
1:02 + 36 = 1:38 PM to be finished
Oh, silly me. I didn't even begin to think about the time it took him to set up! Thank you so much!