Answer:
Rhonda: 39 hours; Chris: 18 hours.
Step-by-step explanation:
If you subtract the extra 3 hours from the total, you have Chris's hours plus twice Chris's hours adding to 54. That is, Chris worked 54/3 = 18 hours, and Rhonda worked 57-18 = 39 hours = 2·18 +3 hours.
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If you insist on equations, you can write two of them:
... r = 2c +3
... r + c = 57
Substitute for r in the second equation:
... (2c +3) +c = 57
... 3c +3 = 57 . . . . . from here down, the explanation above matches this math
... 3c = 54
... c = 54/3 = 18
... r + 18 = 57 . . . . . . substitute for c in the second equation
... r = 57 - 18 = 39
