let 'x' be the number of papers he sold yesterday
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-He sold 65 newspaper today which is 17 more than 3/5 of his sales yesterday
3/5x + 17 = 65
3/5x = 65 - 17
3/5x = 48
3x = 48(5)
3x = 240
x = 80
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Therefore he sold 80 newspapers yesterday.