Given the following exponential function, identify whether the change represents growth or decay, and determine the percentage rate of increase or decrease.

y = 99(1.04)^x

This exponential function represents growth since the base, 1.04, is greater than 1.

To determine the percentage rate of increase, we look at the coefficient of x which is 1.04. This means that for every unit increase in x, y will increase by 4%.

Therefore, the percentage rate of increase is 4%.