6th Grade Working/Engineering Problems: Problem 2

Problem: If A worked on a project, it would take 12 days to complete. If B worked on the same project, it would take 9 days to complete. If A worked on it for a certain amount of days, and then B worked on it for another whole number of days, using a total of 10 days, how many days did A work on it?

Key: Systems of equations, set '1 whole' value

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