2) 21n^2+114n=72 => 21n^2+114n-72=0 => 3(7n^2+38n-24)=0
=> 7n^2+38n-24=0 => 7n^2+42n-4n-24=0 => 7n(n+6)-4(n+6)=0 => (7n-4)(n+6)=0

3) 8x^2+42= 55x => 8x^2-55x+42=0 => 8x^2-48x-7x+42=0
=> 8x(x-6)-7(x-6)=0 => (8x-7)(x-6)=0

4) 3n^2 -14n= -16 => 3n^2-14n+16=0 => 3n^2-6n-8n+16=0
=> 3n(n-2)-8(n-2)=0 => (3n-8)(n-2)=0

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