1 pizza = 9 dollars
1 topping = 1 dollar
1. Let's gather the information
2 Pizzas
One pizza is a pepperoni
The other is a mushroom and green pepper
2. Make an equation for the question
x9 + y1 = ?
x = number of pizzas
y = number of toppings
3. Multiply x and y by the number given
2 x 9 + 3 x 1 = ?
2 x 9 + 3 x 1 = 21
Which means, the two pizzas had costed 21 dollars.