David owns a food truck that sells tacos and burritos. He sells each taco for $4.50 and each burrito for $7.75. Yesterday David made a total of $519.25 in revenue from all taco and burrito sales and there were twice as many tacos sold as there were burritos sold. Write a system of equations that could be used to determine the number of tacos sold and the number of burritos sold. Define the variables that you use to write the system. (Let statments and system of equations)