I am not sure what your value of c means...but we can do without that for the moment.
First draw a figure.
The ratio of the sides of a 30-60 right triangle is 2:1:square root of 3.
Thus in your triangle the altitude (b/2)*squaer root of 3.
The area then is (1/4)cb square root of 3.
You supply what you mean for c and away you go!