Since the variable x is at the exponent, this is an exponential function.
To decide whether an exponential function is a growing or decaying one, we have to look at the base of the exponent.
If the base is between 0 and 1, we have exponential decay
If the base is larger than 1, we have exponential growth.
In your case the base is 3, which is larger than 1, so you have exponential growth.