You can model this problem using the following inequations:y≥10 and 4 * y + 12 * x <400 ... To find the number of pizzas and people, you have to rewrite the inequations as equations and solve the 2x2 system. That is y = 10 and 4 * Y + 12 * X = 400. Clearing from the second equation X, X = 30 results. Therefore, approximately Jhon can have 10 people and 30 pizzas at his party.