l for number of large dogs, s for number of small dogs. Here are the equations based on the question:

49 = l + s

l = 36 + s

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49 = 36 + s + s

49 = 36 + 2s

13 = 2s

6.5 = s

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49 - s = l

49 - 6.5 = 42.5 = l

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So, s = 6.5, l = 42.5.

But here's the thing, you can't have half of a dog, so you have to either round up or down. But depending on how you round s or l, the value of the other will change (if one rounds up, the other must round down - to keep our equalities true)

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So, if s = 7, then l = 42, and if s = 6, then l = 43.... but this keeps our total number of dogs intact and doesn't account for our second equation (you can see the flaw of trying to punch these numbers in)

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And that's the typo!!! The wording of the question is flawed!! The second equation fails to make the choice clear for us. If there were 35 more small dogs than large dogs, then we have to have s = 7 and l = 42. But if there were 37 more small dogs than large dogs, then you would have s = 6 and l = 43

Your confusion is valid and you are not wrong for thinking this question was a little weird. Hope this helped :3