Let the percentage of \\\\(_8^{16}X\\\\) be \\\\(A\\\\) %. Then the percentage of \\\\(_8^{18}X\\\\) be \\\\((100-A)\\\\) %.\\\\(\ herefore\\\\) \\\\(16\ imes\\dfrac{A}{100}+18\ imes\\dfrac{100-A}{100}=16.2\\\\)\\\\(\\implies 1800-2A=1620\\\\)\\\\(\\implies A=90\\\\)So the answer is 90% \\\\(_8^{16}X\\\\) and 10% \\\\(_8^{18}X\\\\)