[tex]18x^3\sqrt{7}[/tex]
1) We can simplify this expression with the aid of the properties of rational exponents/radicands:
[tex]\begin{gathered} 7\sqrt{28x^6}+4\sqrt{7x^6}\:\:\:Factor\:28,divide\:6\:by\:the\:index\:2\:of\:the\:square\:root. \\ \\ 7\cdot\:2x^3\sqrt{7}+4x^3\sqrt{7} \\ \\ 14x^3\sqrt{7}+4x^3\sqrt{7} \\ \\ 18x^3\sqrt{7} \end{gathered}[/tex]
Thus, this is the sum of it in its simplest form.
