ABC received an order to manufacture at least 300 photocopiers. Photocopiers can be manufactured using three assembly methods: manual, mixed and automatic. Assembly costs are $500, $300 and $700 per photocopier using manual, mixed and automatic lines, respectively. Time requirements (in minutes) to staff and the factory floor are described in the following table.

	Manual	Mixed	Automatic
Senior	20	10	15
Junior	40	65	30
Factory floor	70	90	50

ABC has 150 and 110 labour hours of senior and junior staff, respectively. The factory floor is available for 500 hours. The amount of senior staff time used should be at least 30% of the total labour time used.

1) Formulate the Linear Program to minimise the manufacturing cost.

If ABC does not require the factory floor for the whole 500 hours, it may rent it out to other companies for $2.5 per minute.

2) Write down the equation defining S, the unused factory floor time.

3) Modify the objective function to account for the rental option.