Mackenzie and her children went into a movie theater and she bought $99.50 worth of bags of popcorn and candies. Each bag of popcorn costs $8.50 and each candy costs $4. She bought a total of 17 bags of popcorn and candies altogether. Write a system of equations that could be used to determine the number of bags of popcorn and the number of candies that Mackenzie bought. Define the variables that you use to write the system.