Beth bought 20 tickets to a movie, where adult tickets cost $8.00 and senior citizen tickets cost $4.00. she spent a total of $140. which system of equations will determine the number of adult tickets, a, and the number of senior citizen tickets, s, beth purchased?

a + s = 20

8a + 4s = 140

a + s = 140

8a + 4s = 20

a + s = 20

a + s = 140

a + s = 20

4a + 8s = 140

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