4 charges are placed each at a distance ‘a’ from origin. The distance ‘a’ from origin. The dipole moment of configuration is :

As the total charge of the configuration is zero so the origin is independent of choice. Now we can find the dipole moment about given origin. 

Dipole moment about the origin is given by $\overrightarrow{\mathrm{p}}=(-2\mathrm{q})\left(\mathrm{a}\hat{\mathrm{i}}\right)+3\mathrm{q}\left(\hat{\mathrm{j}}\right)+(-2\mathrm{q})(-\mathrm{a}\hat{\mathrm{i}})+\mathrm{q}(-\mathrm{a}\hat{\mathrm{ȷ}})==2\mathrm{qa}\hat{\mathrm{j}}$