production function Q = 6L -0.5L squared
I'm basing this on Q = 6L - (0.5L squared)
and not Q = (6L - 0.5L) squared

I would have to assume the owner wants to have the maximum production, therefore that Q should be the highest number.

When L = 1, Q = 5.75.
L = 2, Q = 11.
L = 3, Q = 15.76
L = 4, Q = 20
L = 5, Q = 23.75
L = 6, Q = 27
L = 7, Q = 29.75
L = 8, Q = 32
L = 9, Q = 33.75
L = 10, Q = 35
L = 11, Q = 35.75
L = 12, Q = 36
L = 13, Q = 35.75
So the correct answer is L (employees) = 12