$A$ and $B$ are two like parallel forces. A couple of moment $H$ lies in the plane of $A$ and $B$ and is combined with them. The resultant of $A$ and $B$ after combining is displaced through a distance:

The resultant of two like parallel forces $A$ and $B$ is $A+B$.When a couple of moment $H$ is added to the system, the magnitude of the resultant remains the same ($A+B$), but its point of application shifts.The displacement $d$ is given by the relation:Resultant $\times d=H$$(A+B)d=H⟹d=\frac{H}{A+B}$.