In an assignment of mine we are required to plot a graph and it's table of values, the problem I'm having is the values must not be in decimal form, so for example;

If I have the function below, and I need to find the value for y, if x=-2 how do I find that without it turning it into a decimal. The answer in the practice question says Y=-7/9. I think I understand where the 9 came from, but thats about it (3^{-2}= 1/9)

y = 2(3)^{x }– 1

Anyone care to explain?