Her recipe calls for 1/4 cup of juice but she wants to double that so she needs 1/4+1/4 = 1/2 cup of lime juice
16 tablespoons are in 1 cup and she only needs 1/2 cup so she needs 16*.5 = <<16*.5=8>>8 tablespoons of juice
1 key lime yields 1 tablespoon of juice and she needs 8 tablespoons so she needs 1*8 = <<1*8=8>>8 key limes
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