There is not enough information here to solve this problem.
For example: Carlos 14, Maria 21 or Carlos 15, Maria 22.
For any real positive number x Carlos can travel x km/h and Maria (x + 7) km/h.
If you had given a distance for Maria, or time for one of them I could have answered your question, but without some critical additional information this problem cannot be solved. That means that there are infinitely many solutions without another critical piece of information.
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