Sadie runs a farm stand that sells bananas and grapes. Yesterday Sadie sold 13 pounds of bananas and 15 pounds of grapes for a total revenue of $55.50. Today she sold 46 pounds of bananas and 16 pounds of grapes for a total revenue of $131.50. Write a system of equations that could be used to determine the price of each pound of bananas and the price of each pound of grapes. Define the variables that you use to write the system.