Therefore, together a lemonade and a cookie cost 60 cents.

Alternatively, since this problem is looking for the value of (m + c), we can add the two initial equations together:

7m + 7c = 4.20

If we now factor out a 7 on the left:

7(m + c) = 4.20 7(m + c) / 7 = 4.20 / 7 (m + c) = .60

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