Answer:

Step-by-step explanation:
REFER THE ATTACHED FIGURE
Given :
AC and DB are parallel bars .
AB is the diagonal between two parallel bars .
The angle made by the diagonal with the parallel bar on top is 60 degrees.
The distance between the two parallel bars is 9 feet.
To Find : What is the length of the support AB?
Solution :
For ∠BAC = 60° base is AC and perpendicular is BC
Using trigonometric ratios i.e.




Thus Option 4 is correct
Length of support AB = 9 divided by sin 60 degrees