Max is organising a trip to the airport for a party of 75. he can use two types of taxi.
a small taxi costs $40 for the trip and holds up to 4 people.
a large taxi cost $63 for the trip and holds up to 7 people.

1. (a) if max orders 6 large taxis, how many small taxis will he need?
(b) how much will the total cost be?

2.max can organise the journey more cheaply than this!
how many taxis of each type should max order, to keep the total cost as low as possible?