Game: Resulting force

Your boat broke down and two friendly rowers are going to help you. [br]They are pulling with the forces [math]\text{\vec{a}}[/math] and [math]\text{\vec{b}}[/math].[br]Calculate the resulting force [math]\text{\vec{a}}+\text{\vec{b}}=\text{\vec{c}}[/math] untill you got 5 Points.[br]

Information: Game: Resulting force