Correct. Thinking about each machine in terms of their hourly rate, you find that one can install 7.5 per hour and the other can install 12.5 per hour, so together they can install 7.5+12.5=20 each hour. Setting up the equation $\displaystyle\frac{{20}}{{1}}=\frac{{300}}{{h}}\usepackage{cmbright}\Huge\$ , you find h=15.