For a wind speed of 6 m/s, a stack gas exit velocity of 20 m/s, a stack diameter of 4 m, a heat emission rate of 15 MW, and an ambient pressure of 950 mbar, calculate the final plume rise in a natural atmosphere using (a) the Holland; (b) the modified Concawe; and (c) the Briggs method. Assume the stack gas has a molecular weight of 28.9 g/mole. Discuss the practical implication/meaning of the variation among these models.