Hello!
To solve this we use the equation sin60 = (s/2) / (d/2)
s is a side of the triangle
d is the diameter
sin60 = s/d
[tex] \sqrt{3/4} =s/d[/tex]
[tex]d=s/ \sqrt{3/4} [/tex]
[tex]d = s \sqrt{4/3} [/tex]
[tex]d = 2s/ \sqrt{3} [/tex]
put 6 in for s
[tex]d=12/ \sqrt{3} [/tex]
[tex]d = \sqrt{48} [/tex]
d = 6.9
The answer is C) 6.9
Hope this helps!