A body is in equilibrium under the influence of three forces. Two of these forces act in directions inclined at 60 degrees. To one another and their magnitudes are 40 N and 30 N respectively. Find the magnitude and direction of the third force.

Help!! I have no clue where to even begin..

I answered a very similar question that you posted in the physics forum - see: https://www.askmehelpdesk.com/physics/force-473309.html