Molarity = moles of solute/volume of soln. in ltres.
9 mol/litre = (w/50)/(m/d)...................................(1)
10 molality means 10 moles are present in 1 kg water.
molar mass = 500 gm is present in 100 gm water.
mass of solution = 1500 gm.
Volume = 9M/10mol and volume = 1.1111 l
density comes to = 1500/1111 = 1.350 g/l