## Elementary Algebra

$(x+y)(5+a)$
Upon inspection, we find that $5$ is common to the first two terms of the expression while $a$ is common to the last two terms of the expression: $5x+5y+ax+ay$ =$5(x+y)+a(x+y)$ Since $(x+y)$ is now common to the expression, we factor it out: $5(x+y)+a(x+y)=(x+y)(5+a)$ The expression cannot be factored further.