Mr and Mrs Waugh wanted to use a caterter for a birthday party for their twin sons. The manager said that the cost for a family og four is $160. However, the sons wanted to invite 8 friends, making 12 people in all, and for this would be $360. If the total cost in each case is made up of the same cost per person and thsame fixed cost, find the cost per person and the fixed cost.

Cost function is:

y = F + Vx

(Though I didn't write it as a function per se - just easier using y.)

Variable costs are those that happen for each individual thing. This is something appied in cost accounting a lot. So if variable costs were $10 per unit produced, then you'd take the $10 and multiply by the total units produced to get total variable costs. Then fixed costs are those that don't change no matter what. Like the secretary's salary. (In this case, things like the gas and depreciation on the truck will be the same no matter how many people are there.) So you don't multiply by anything in this case. It's just one lump sum fixed amount.

Which is where F + Vx comes from.

Try to set up your equations first.