$$\sqrt[k]{\frac{49^{K+\frac{1}{4}}\sqrt{7.7^{-K}}}{7\sqrt{7^{-K}}}=x.$$
$x=\left(\frac{7.7^{-\frac{k}{2}}\times 7^{\frac{5k+1}{2}}}{7}\right)^{\frac{1}{k}}$
$k\neq 0$
