We know that the general form of the exponential equation is . We also know that when a>0 and 0<b<1, then this exponential equation will represent an exponential decay.
Now, the expression given to us is
As we can see from this equation, a=5.8>0, and , thus, 0<b<1, since, and thus, as per the general form, the given equation represents exponential decay.
For a better understanding of the explanation provided here, the graph of has been attached. As can be seen from that graph it indeed is an exponential decay.