Really dumb question - Percentage increase\decreased calcualtion

I have a simple enough question but cant seem to work out how to get it right.

I cant to calculate the percentage increase (or decrease) between the 2 numbers in each row and put that into column E on the same row.  I'm guessing put a formula in cell E1 and then cascade that formula down.

If there is a 0 in any of the cells e.g. rows 3 and 4 I want a N\A or something like that in the calculation because there is no data available yet.

Please help.