ПОМОГИТЕ РЕШИТЬ.......

Решите задачу:

$1) \\ ( \frac{x}{5}+ \frac{x}{2} )* \frac{10}{a^2} \\ \\ ( \frac{2x}{10}+ \frac{5x}{10} )* \frac{10}{a^2} \\ \\ \frac{7x}{10}* \frac{10}{a^2} = \frac{7x}{a^2} \\ \\ 2) \\ (1- \frac{1}{a}): \frac{a-1}{3a^2} = (\frac{a-1}{a} ): \frac{a-1}{3a^2} = \frac{(a-1)}{a} * \frac{3a^2}{(a-1)} =3a \\ \\ 3) \\ (1+ \frac{y}{x}):( \frac{y}{x} -1)=( \frac{x+y}{x}) :( \frac{y-x}{x})= \frac{(x+y)}{x} * \frac{x}{(y-x)}= \frac{x+y}{y-x}$