The constant price is 18 dollars, which never changes and for every topping you get, it costs $ 1.50. Since we don't know how many extra toppings are added we write 1.50c. This shows that the price will be determined by the number of extra toppings added. If you got no toppings, sub in 0 for c to get $ 18 .
The base price of the large cheese pizza is $18. Since we don't know how many extra toppings are added we write 1.50c. This shows that the price will be determined by the number of extra toppings added. Since the question asked for an expression and not an equation, there is no equals sign.
