Sheila budgets $9 per week for her morning coffee with milk. She likes it only if it is prepared with 4 parts of coffee and 1 part milk. Coffee costs $1 per ounce and milk costs $0.5 per ounce. How much coffee and how much milk will Sheila buy per week? How would your answer change if the price of coffee rises to $2 per week? Illustrate your answers graphically.