This function doesn't make sense, unless you make it f(t)=225(1.23)^x. I will assume that you forgot to add the x squared. The rate of decay is 23%. Since the base is between 1 and 0, it is an exponential decay and you'll need to subtract the r-value with 1. (If it were an exponential growth, you would have to add 1.) The initial value or the a-value is 225.
