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Решите задачу:

$1) \frac{ {a}^{2} - 25 }{a + 3} \times \frac{1}{ {a}^{2} + 5a } = \frac{(a - 5)(a + 5)}{(a + 3) \times a(a + 5)} = \frac{a - 5}{a(a + 3)}$
$2) \frac{ {a}^{2} + 10a + 25 }{ {a}^{3} - 6a + 9a} \div \frac{a + 5}{a - 3} = \frac{ {(a + 5)}^{2} (a - 3)}{a(a - 3) ^{2}(a + 5) } = \frac{a + 5}{a(a - 3)}$
$3) \frac{a - 5}{a(a + 3)} - \frac{a + 5}{a(a - 3)} = \frac{ - 10}{a(a - 3)}$
$4) \frac{ - 10}{a(a - 3) } + ( \frac{4}{a - 3} ) ^{2} = \frac{ - 10 }{a(a - 3)} + \frac{16}{(a - 3) ^{2} } = \frac{ - 10a + 30 + 16a}{a {(a - 3)}^{2} } = \frac{6(a - 5)}{a {(a - 3)}^{2}}$