A rectangular tank 3.6 m long and 1.8 m wide is divided into two parts, by a vertical dividing plate so that the capacity of one portion is twice that of the other. The dividing plate has a hole 25 mm square near the bottom, forming a submerged orifice. At first the level of the water in the larger portion is 1.8 m above that in the smaller. Determine the time taken for this difference of level to be reduced to 0.9 m. Cd=0.6