A bookstore charges a standard rate for paperback or hardback books. The cost of a paperback book is 4 dollars less than the cost of a hardback book.​ Recently, one day of sales totaled ​$1065.10. That day the bookstore sold 51 paperback books and 47 hardback books. Write a system representing this situation. Use the graph to estimate the solution of the system. What does the solution mean in this​ situation? How much does each type of book​ cost? Use substitution to verify your solution.