A Whoppa pizza base is made using one of 2 types of cheese and one of 2 toppings. Up to 3 additional toppings are available at extra cost. The number of different Whoppa pizzas that can be made containing at least one additional topping is:
A) 12 B) 16 C) 24 D) 28 E) 20
I know the answer to this question but I don't how you get the answer. So, I would like to see it done correctly showing any working out.