A student bought a calculator and a textbook for a course in algebra. He told his friend that the total cost was $115 (without tax) and that the calculator cost $20 more than four times the cost of the textbook. What was the cost of each item? Let x= the cost of a calculator and y= the cost of the textbook. The corresponding modeling system is {x+y=115x=4y+20. Solve the system by using the method of substitution.