Ok, so
Let me draw the situation here below:
For this problem, we have to use the trigonometric relations.
In this case, it would be useful to use sin(x).
Sin(x) relations the opposite side of the angle and the hipotenuse of the triangle so:
Sin(60) = (7√3) / c
And c = (7√3) / Sin(60)
Remember that sin(60) is a number, whose value is √3/2.
So,
And finally, c = 14 feet