Halfway towards her goal is $45 because 90 / 2 = <<90/2=45>>45
She sells $35 worth of books before she loses the money because 45 - 10 = <<45-10=35>>35
She sells 7 books before losing her money because 35 / 7 = <<35/7=5>>5
She then sells 18 books because 90 / 5 = <<90/5=18>>18
She sells 25 books in total because 18 + 7 = <<18+7=25>>25
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