Прошу помогите((Алгебра..

Упростим выражение:
$\frac{y^2-6y+9}{y^2-9} : \frac{10y - 30}{y^2 + 3y} = \frac{y^2-2*y*3+3^2}{y^2-3^2} : \frac{10(y-3)}{y(y+3)} = \frac{(y-3)^2}{(y-3)(y+3)} * \frac{y(y+3)}{10(y-3)} = \\ \\ = \frac{y-3}{y+3} * \frac{y(y+3)}{10(y-3)} = \frac{y(y-3)(y+3)}{10(y-3)(y+3)} = \frac{y}{10} = \frac{1}{10} *y = 0.1y \\ \\$

при у =70 ⇒ 0,1 × 70 = 7