Chris purchased a new mattress for $1,399. He will need to pay $78 each month on his interest-free loan to pay off the total price of the mattress in 18 months. Separately, Chris sets aside $50 each month in a savings account, which currently shows a balance of $250. Create an augmented matrix from a system of equations to help Chris determine when he can use monthly payments and savings to pay off the total purchase price of the mattress.