Two identical elastic strings of negligible relaxed lengths are tied at fixed points A and B at their one of the ends. Their other ends are tied to a small ball. The system is in gravity free space. To hold the ball in equilibrium at point (4m, 3m) an external force of magnitude F = 1000N is required. Then the force constant k of the strings is k = 20n (in N/m) then find n = ?