Answer:
9
Step-by-step explanation:
For each pizza variety, Daniel can choose 18 different toppings. Therefore, for 23 pizza varieties, Daniel can choose from 23 * 18 = 414 different combinations of varieties and toppings.
For each pizza size, Daniel can choose from 414 different combinations of varieties and toppings. Therefore, for n pizza sizes, Daniel can choose from n * 414 = 3726 combinations
414n = 3726
divide both sides by 414 to isolate the n
n = 9