For a reaction X + Y ⇌ 2Z , 1.0 mol of X, 1.5 mol
of Y and 0.5 mol of Z were taken in a 1 L vessel and
allowed to react. At equilibrium, the concentration
of Z was 1.0 mol L^–1. The equilibrium constant of reaction
is $${x \over {15}}$$. The value of x is _________.