Janet, Rosi, and Tanya buy postcards from their favorite souvenir shop. Janet buys 3 postcards for $1.05. Rosi buys 5 postcards for $1.75. Tanya buys 8 postcards for $2.80. Are the cost, y, in dollars and the number of postcards, x, proportional? Explain your answer. Write an equation to represent this relationship, if possible. Lesson 2-4