Michael went to the grocery store and bought bottles of soda and bottles of juice. Each bottle of soda has 40 grams of sugar and each bottle of juice has 20 grams of sugar. Michael purchased a total of 11 bottles of juice and soda which collectively contain 300 grams of sugar. Write a system of equations that could be used to determine the number of bottles of soda purchased and the number of bottles of juice purchased. Define the variables that you use to write the system.