Final answer:
The correct system of equations to find the number of adult and student tickets Mr. Robinson purchased is a+s=9 and 3a + 4s = 31.
Step-by-step explanation:
The correct system of equations that can be used to find the number of adult tickets (a) and the number of student tickets (s) Mr. Robinson purchased is B) a+s=9 and 3a + 4s = 31.
In the first equation, a+s=9, the sum of the number of adult tickets (a) and the number of student tickets (s) is equal to 9, which represents the total number of tickets purchased.
In the second equation, 3a + 4s=31, the price of the adult tickets (3a) and the price of the student tickets (4s) is equal to the total amount of money spent, which is $31.