4. [8 marks] 400 tickets were sold for a local comedy festival. Box seats were $12, orchestra seats were $10, and balcony seats were $8. The total income from ticket sales was $3700 and the combined number of orchestra and balcony seats was 7 times the number of box seats sold. (a) Set up a system of three equations representing this situation. Make sure to clearly assign variables to each unknown quantity. (b) Use matrices to determine how many seats of each type were sold. Include a concluding statement in your solution