Idrees engineering (IE is a supplier of various types of industrial machines. It also provides services for the maintenance of these machines. Following transactions were carried out by IE during the year ended 30 June 2017: Five machines where are sold on a lay away basis to one of its frequent customers. Three out of a total of 5 installments had been received till the year end. A service contract for maintenance of a machine for a period of one year was signed and IE received a non-refundable annual fee amounting to Rs. 45,000 as advance on 15 April 2017. Required: Discuss when it will be appropriate for SE to recognize revenue in each of the above situation.