Correct. The value under the radical in a square root function cannot be less than 0. So the domain is all x-values for which the radicand is not negative. That means $\displaystyle{6}{x}-{24}\ge{0}\usepackage{cmbright}\Huge\$ . So $\displaystyle{6}{x}\ge{24}\usepackage{cmbright}\Huge\$ , and therefore $\displaystyle{x}\ge{4}\usepackage{cmbright}\Huge\$ . The domain is $\displaystyle{x}\ge{4}\usepackage{cmbright}\Huge\$ .