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**Big_Joe** Hey i am stuck on this question i have found in a past paper can someone please help me solve this asap as i have a mechanics exam tomorrow and i need to be able to do all topics as well as possible:

A steel girder AB has a weight 210N. It is held in equilibrium in a horizontal position by two vertical cables. One cable is attatched to the end A. The other cable is attatched to the point C on the girder, where AC = 90cm. The girder is modeled as a uniform rod, and the cables as light inextensible strings.

Given that the tension in the cable at C is twice the tension in the cable at A, show that AB = 120cm.

Thanks to anyone who helps.