Just type it straight in like this!
You can use the buttons on the calc or you can just type it in from your keyboard.
the calc is pretty snazzy like that!
e^(-1.5)=
$${{\mathtt{e}}}^{\left(-{\mathtt{1.5}}\right)} = {\mathtt{0.223\: \!130\: \!160\: \!148\: \!429\: \!8}}$$