this is nuts... the husband and I are disagreeing on how to workt his out for the kiddo. How would you work out this problem? Obviously we know she spent 10 dollars, but we cannot agree on how to come ...

I'll assume you don't have the equation for these values. Are thye liner? Exponential? An easy way is to put them into excel and graph them. Then add a trend line and have it show the trend line ...