Xavery is one of the lawn service customers. She will be on vacation for a month. Normally, the lawn is mowed weekly. Each time the lawn is mowed, the fee is $50. Xavery has sent you a check (#451) for $200 for the four weeks in August. She has requested that you mow the lawn as normal while she is on vacation. In order to record revenue, what must take place? Did this take place?What accounting principle governs when something is declared as revenue?