Answer: 4
<u>Step-by-step explanation:</u>
To fit the maximum amount of people in one row, you would have 3 couples and 1 single = 7 parents.
If we continue the maximum amount of people for 7 rows, we get 49 parents seated.
Since a total of 54 parents are seated, that leaves 54 - 49 = 5 parents remaining to be seated in the last row. These parents can be seated as 2 couples and 1 single. If you put the single at the end of the row, there will be 4 seats between the couple and the single.
Couple, Couple, Open, Couple, Couple, <u>Open</u>, <u>Open</u>, <u>Open</u>, <u>Open</u>, Single