The number 1.04 represents the rate at which the house appreciates, or increases in its price annually.
As according to the values of an exponential equation, which is represented by this: y=ab^x, the a value represents the original price, the b value represents the rate of growth/decay (if growth, you add 1 to the rate, if decay, you subtract the rate from 1), and x represents the amount of times it decays or grows.
As according to the function f(x) = 242,000(1.04)^x, 242,000 is the original price and 1.04 is the rate of growth since 1 has been added to the the 4% annual growth.