When an exponential function is given as
f(x)=ab^x, and
knowing that b^0=1, that means that
f(0)=ab^0=a value of function when x=0, or the initial value.
In the case of
f(x)=20.b^x, f(0)=20.b^0 = 20 (initial value)
If b=1.2, then the hourly growth rate is (1.2-1)=0.2=20%.
If b=1.85, then the hourly growth rate is (1.85-1)=0.85=85%.