Answer:

[tex]\tt B)\:x^2+16[/tex]

Step-by-step explanation:

[tex]\tt 1)\:x^2 - 36[/tex]

[tex]\tt x^2-6^2[/tex]

[tex]\tt \left(x+6\right)\left(x-6\right)[/tex]

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[tex]\tt 2)\:x^2 + 6[/tex]

*Can't be factored out anymore*

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[tex]\tt 3)\:x^2-7x+12[/tex]

[tex]\tt \left(x^2-3x\right)+\left(-4x+12\right)[/tex]

[tex]\tt x\left(x-3\right)-4\left(x-3\right)[/tex]

[tex]\tt \left(x-3\right)\left(x-4\right)[/tex]

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[tex]\tt 4)\:x^2-x-20[/tex]

[tex]\tt \left(x^2+4x\right)+\left(-5x-20\right)[/tex]

[tex]\tt x\left(x+4\right)-5\left(x+4\right)[/tex]

[tex]\tt \left(x+4\right)\left(x-5\right)[/tex]

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Hope this helps!

Have a great day!