Algebra
# Polynomial Factoring

If $x=18,$ what is the value of $\frac{x^3-4x^2-21x}{x^2-7x} ?$

If $x:y=4:7,$ what is the value of $\frac{5x^2+xy+y^2}{x^2+y^2}?$

If $x=13,$ what is the value of $\frac{x^2+7x-8}{x^2-6x+5} \times \frac{x^2-4x-5}{x^2+9x+8} ?$

If $\frac{x+4}{x^2+3x-4}=a,$ what is the value of $a$ when $x=\frac{14}{13}$?