A pencil last 7.5 hours because 5 x 1.5 = <<5*1.5=7.5>>7.5
The pencils she has will last 75 hours because 10 x 7.5 = <<10*7.5=75>>75
She needs 30 more hours of writing because 105 - 75 = <<105-75=30>>30
She will need 4 more pencils to reach this because 30 / 7.5 = <<30/7.5=4>>4
She will spend $8 on pencils because 4 x 2 = <<4*2=8>>8
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