A mass m1 is attached to a wire of linear density 5.4 g/m, and the other end of the wire run over a pulley and tied to a wall as shown in Fig. The speed of transverse waves on the horizontal section of wire is observed to be 20 m/s. If a second mass m2 is added to the first, the wave speed increases to 45 m/s. Find the second mass. Assume the string does not stretch appreciably.