Two elastic strings, A and B, stretch by 30mm and 60mm respectively when a weight of 4N is attached to each in turn. the strings are hung vertically from the same point, close together, so that when they are unstretched the lower end of A hangs 30mm below that of B. The lower ends are now attached together to a weight of 6N. Find the tension in each string when the weight is hanging in equilibrium.
I have found the two moduli of elasticity in terms of $l_A$, the natural length of string A. Can I consider A and B to be one string? If so how can I find the tension in each string?
$\lambda_A = (2/15)l_A$
$\lambda_B = (1/15)l_A-2$