When it gets to the part of the equation I need to find out what F equals.

(Square root of 3) / 2 = 19.5 / F

I don't understand how to get F.

I know the answer is 13 (Square root of 3).

I need to know how this is solved...

Can anyone show the steps how I can get this answer? I have a Ti-84+ encase it might help.