[tex]( \frac{3 {x}^{4} }{ {a}^{5} } ) {}^{5} \times ( \frac{a {}^{6} }{3 {x}^{5} }) {}^{4} = \frac{ {3}^{5} \times {x}^{20} \times a {}^{24} }{ {3}^{4} \times {a}^{25} \times {x}^{20} } = \\ \frac{3}{a} = 3 \div ( - \frac{1}{7} ) = 3 \times ( - 7) = - 21[/tex]