Помогите пожалуйста,срочно! Упростите:

$\frac{x^2-4x}{x^2+7x}:\frac{24-6x}{49-x^2}=\frac{x(x-4)}{x(x+7)}*\frac{(7-x)(7+x)}{6(4-x)}= -\frac{x-4}{1}*\frac{7-x}{6(x-4)}=-\frac{7-x}{6}$

$\frac{y^3-16y}{2y+18}:\frac{4-y}{y^2+9y}=\frac{y(y^2-16)}{2(y+9)}*\frac{y(y+9)}{4-y}=-\frac{y(y-4)(y+4)}{2}*\frac{y}{y-4}=$

$=-\frac{y^2(y+4)}{2}$

$\frac{(a+b)^2-2ab}{4a^2}:\frac{a^2+b^2}{ab}=\frac{a^2+2ab+b^2-2ab}{4a^2}*\frac{ab}{a^2+b^2}=\frac{a^2+b^2}{4a}*\frac{b}{a^2+b^2}=\frac{b}{4a}$

$\frac{5c^3-5}{c+2}:\frac{(c+1)^2-c}{13c+26}=\frac{5(c-1)(c^2+c+1)}{c+2}*\frac{13(c+2)}{c^2+2c+1-c}=$

$=\frac{5(c-1)(c^2+c+1)}{1}*\frac{13}{c^2+c+1}=65(c-1)$