You may have tried to find the combined rate of the machines by adding the number of widgets and adding the times and then dividing. The old machine's rate is $\displaystyle\frac{{24}}{{3}}\usepackage{cmbright}\Huge\$ or 8 widgets per hour. The new machine's rate is $\displaystyle\frac{{48}}{{4}}\usepackage{cmbright}\Huge\$ or 12 widgets per hour. You need to add these to find their combined rate.