Answer
a. $x^2+7x+12$
b. $x^2+25x+100$
Work Step by Step
a. $(x+3)(x+4)$
Use the Distributive Property:
$(x+3)(x+4)=x(x+4)+3(x+4)$
$=x^2+4x+3x+12$
$=x^2+7x+12.$
b. $(x+5)(x+20)$
Use the Distributive Property:
$(x+5)(x+20)=x(x+20)+5(x+20)$
$=x^2+20x+5x+100$
$=x^2+25x+100.$
