Audrey runs a farm stand that sells apples and raspberries. Each pound of apples sells for $1.75 and each pound of raspberries sells for $1.25. Audrey made $124.50 from selling a total of 80 pounds of apples and raspberries. Write a system of equations that could be used to determine the number of pounds of apples sold and the number of pounds of raspberries sold. Define the variables that you use to write the system.