Camila and her children went into a bakery and she bought $35 worth of cupcakes and brownies. Each cupcake costs $3.75 and each brownie costs $2.50. She bought a total of 10 cupcakes and brownies altogether. Write a system of equations that could be used to determine the number of cupcakes and the number of brownies that Camila bought. Define the variables that you use to write the system.