a. abc x 9 = 6abc
abc x 9 = 6000 + abc
abc x 9 - abc = 6000
abc x 8 = 6000
abc = 750
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b. abc x 6 = 4abc
abc x 6 = 4000 + abc
abc x 6 - abc = 4000
abc x 5 = 4000
abc =800
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c.5abc=abc x 9
5000 + abc = abc x 9
5000 = abc x 9 - abc
5000 = abc x 8
abc = 625