The entire sq ft of the living room is LxW so the room is 16x20 = <<16*20=320>>320 sq ft
Tom has already put down 250 sq ft so he needs to put down 320-250 = 70 sq ft of flooring
The boxes contain 10 sq ft of flooring per box and he needs 70 more sq ft of flooring so he needs 70/10 = <<70/10=7>>7 more boxes
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