I think since there's two different groups so you divided 83 into those two groups which gets you 41.5. Then you subtract 15 from the 41.5, that gets you 26.5. Once you finish subtracting you will subtract 26.5 from 83 which gets you 56.5. After that add the 56.5 & 26.5 together to see and that gets you ,your 83. I think it might be wrong
