Correct. Setting up an equation that relates Rocco's rate of work (1 room in 6 hours), Sam's rate of work (1 room in 5 hours), Tanaka's rate of work (2 rooms in 15 hours), and the group's rate of work (3 rooms in x hours), you find $\displaystyle\frac{{1}}{{6}}+\frac{{1}}{{5}}+\frac{{2}}{{15}}=\frac{{3}}{{x}}\usepackage{cmbright}\Huge\$ . Solving for x yields x=6.