A shop is selling sandwiches.

The cost that is involved amounts to $50 plus $.80 per sandwich. If the manager charges $x for each sandwich, where x = 3.5 - 0.01n and n is the number of sandwiches.

Firstly I'm having trouble finding the expression for the revenue and for costs as functions of n.

Also I can't seem to work towards this part of the question either.

Show that an expression for the profit $P made from selling n sandwiches is

P = 2.7n-0.01n^2-50