For a floral arrangement class, Jayvon has to create an arrangement of twigs and flowers that has a total of 9 objects. Jayvon has to pay for the twigs and flowers that he uses in his arrangement. Each twig costs $1, and each flower costs $3. He spends a total of $15 on the twigs and flowers. Write and solve a linear system to find the number of twigs and the number of flowers he used. Use the method of substitution.​