Considering that the hallway is rectangular in shape such that its perimeter is calculated by the equation,
P = 2L + 2W
where P is perimeter, L is length, and W is width. Substituting the known values,
10.4 = 2L + 2W
Dividing both sides of the equation by 2,
5.2 = L + W
W = 5.2 - L
