<span>for that, what you need is a calculator... like say a TI(texas instruments) 83 or 83plus or higher, will do regressions, if you have an android device like a phone or tablet, you can also get an app from the play store "Andie's graph", is a TI calculator emulator, it works just like the calculator itself, you'd only need the ROM
</span><span>that said, you can also use some online calculators for that. </span> <span>I could give you a direct link to one, but this site has issues with links, if you do a quick search in google for "keisan exponential regression calculator", it should be the first link, is from the Casio site. </span> <span>you could do regressions in a spreadsheet as well.... you could check online for an "addin" or "extension", if you use MS Excel, pretty sure there are some addins for regressions. </span> if I recall correctly, Excel does regressions natively, but the addins are just frontends, is all, just some added interfacing.
anyhow, if you have an Android device Andie Graph works peachy, I have an 83plus, 84, 86 in it, they all work just like my old TI83plus.
there's also an app in the play store called Graph89, is an emulator for a TI89, the same you need a tiny little file, and texas instruments provides them, have also, works peachy too.
To find the percentage, you divide the new price ($39.90) by the original price ($38), and the multiply it by 100 to change the answer from a decimal to a percentage:
39.90 / 38 x 100 = 105
So 39.90 is 105% of 38
To get our final answer, subtract this by 100%
105 - 100 = 5%
ANSWER: So the percentage increase of the price is 5% ($1.90)