a lamp is supported in equilibrium by two chains fixed to two points A and B at the same level; the lengths of the chains are 0.3m and 0.4m and the distance between A and B is 0.5m. Given that the tension in the longer chain is 36N, show by resolving horizontally that the tension in the shorter chain is 48N,. By resolving vertically, find the mass of the lamp.

I havent gotten past the first problem, proving that the tension in the first chain is 48N. I'm guessing that geometry comes in somewhere cos they gave the lengths of the chains but i couldnt say how, and i dont comprehend the relationship between the tensions in the chains; how is the lamp in horizontal equilibrium?