Answer: (x+3)(x+4)
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Step-by-step explanation:
Erase the common (x+4) terms. We're left with x+3
So it factors to (x+3)(x+4)
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Another approach:
Let y = x+4
x(x+4)+3(x+4)
xy + 3y ... replace each x+4 with y
(x+3)y .... factor using the distributive property
(x+3)(x+4) ... replace y with x+4
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Checking the answer:
You can use the FOIL rule to get
(x+3)(x+4) = x^2+4x+3x+12
Then factor an x out of x^2+4x to get x(x+4)
Also, factor 3 from the remaining terms to get 3(x+4)
This shows that x(x+4) + 3(x+4) = (x+3)(x+4) is an identity.
Another way to check the answer is to follow the steps shown in the second section, but do so in reverse. This means you'll start at the last step and work your way up.