Hello there! :D
Well, it is a general rule of thumb that growth is indicated by positive numbers, and decay is indicated by negative numbers. I would show decay in this exponential equation by making the percentage inside the parenthesis negative. It would look like this: y=4800(-1.239)
Obviously, this equation does not have a negative integer so we know it must constitue growth!
I hope this helped you and that you have a wonderful day,
Kai xx