Correct. Using the equation for work, $\displaystyle{r}=\frac{{W}}{{t}}\usepackage{cmbright}\Huge\$ , you find that the rate of A is $\displaystyle\frac{{1}}{{4}}\usepackage{cmbright}\Huge\$ , the rate of B is $\displaystyle\frac{{1}}{{h}}\usepackage{cmbright}\Huge\$ , and the rate of C is $\displaystyle\frac{{1}}{{{2}{h}}}\usepackage{cmbright}\Huge\$ . If it takes all three mowers one hour to do the job together, then $\displaystyle\frac{{1}}{{4}}+\frac{{1}}{{h}}+\frac{{1}}{{{2}{h}}}=\frac{{1}}{{1}}\usepackage{cmbright}\Huge\$ . Solving for h, you find h=2.