At to-go pizza each pizza cost $12 and each small salad costs $2. a delivery charge of $3 is added to every order. how much would it cost to have 6 pizzas and 3 small salads delivered?

First, let's make some variables then make an expression. 

Let x = the number of pizzas
Let y = the number of salads

Then 12x = the price for x pizzas
Then 2y = the price y pizzas

Now we can make our expression.

We combine the costs for the pizzas and salads and delivery charge is added.

12x + 2y + 3

Now we have our expression. Replace the x with how many pizzas you bought and replace the y with how many salads you bought.

How much would 6 pizzas and 3 small salads would cost?

12(6) + 2(3) + 3 = 
72 + 6 + 3 =
78 + 3 =
81

The answer to this question is $81.

EDIT:

I want to give a thank you to Irspow for finding my error!

C=12p+2s+3

if p=6 and s=3 then

c=12(6)+2(3)+3

c=72+6+3

c=$81.00