First find how far Marsha drives to deliver the third package: 28 miles / 2 = <<28/2=14>>14 miles
Then find how many miles she drives total by adding the miles for the three legs of her journey: 14 miles + 28 miles + 10 miles = <<14+28+10=52>>52 miles
Then divide her total pay by the number of miles she drives to find her pay per mile: $104 / 52 miles = $<<104/52=2>>2/mile
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