help with formula's

I have a sheet with a list of cities populations in two different years. 

I need to get an average increase in the percentage for each one. I was given an answer to the first one. and I am able to do the math manually to get a relatively close answer. I cannot seem to get a formula to work at all... 

ex. 

c19 is 149855 and d19 is 140275 the answer is supposed to be 6.8% 

I am sure there is a simple way to do this, I have tried everything I know and get nowhere. 

thanks for any advice.