Answer
$64y^2+9x^2-48xy-49$
Work Step by Step
$ [8y + (7 - 3x)][8y - (7 - 3x)] $
$=(8y+ 7 - 3x)(8y - 7 - 3x)$
$=64y^2-56y-24xy+56y-49-21x-24xy+21x+9x^2$
$=64y^2+9x^2-48xy-49$
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