Beth bought 15 tickets to a movie, where adult tickets cost $6.00 and senior citizen tickets cost $4.00. She spent a total of $76. Which system of equations will determine the number of adult tickets, a, and the number of senior citizen tickets, s, Beth purchased?a. a + s = 766a + 4s = 15c. a+s=154a + 6s = 76b. a + s = 156a + 4s = 76d. a + s = 766a + 4s = 15