If \({[{\{ {(\frac{2}{3})^3}\} ^{(2x + 3)}}]^{\frac{{ - 3}}{4}}} = {[{\{ {(\frac{2}{3})^{\frac{2}{3}}}\} ^{(3x + 7)}}]^{\frac{{ - 6}}{5}}}\), then the value of \(\sqrt {2 - 42x}\) is: