Answer:
230 tickets were sold at door and 170 tickets were sold in advance.
Explanation:
Let x represent the number of tickets sold at the door.
Let y be the tickets sold in advance.
Equations form as per given scenario are:
or x=400-y ......(1)
......(2)
Substituting the value of x from (1) in (2)

=>

=>

We get y = 170
And x =
= 230
Hence, 230 tickets were sold at door and 170 tickets were sold in advance.