Courtney works for the Red Cross and has been tasked with buying non-perishable items for families recently displaced by a hurricane. She finds a company willing to send her Meals-Ready-to-Eat (MREs) at a discounted price. Cases of small portion meals are $20.00 each and cases of large portion meals are $30.00 each. She buys a total of 20 cases and spends a total of $450.00. Let x represent the number of small portion meals and let y represent the number of large portion meals. Write a system of equations, in terms of x and y, to model the situation. Enter your equations in the space provided.