Potential Due to an Electric Dipole

Figure shows a charge array known as an electric quadrupole. For a point on the axis of the quadrupole, obtain the dependence of potential on $r$ for $\frac{r}{a}>>1$, and contrast your results with that due to an electric dipole, and an electric monopole (i.e., a single charge).

Two charges $-\mathrm{q}$ and $+\mathrm{q}$ are located at points $\left(0 , 0 , -\mathrm{a}\right)$ and $\left(0 , 0 , \mathrm{a}\right)$ respectively. How much work is done in moving a small test charge from the point $\left(5, 0 , 0\right)$ to $\left(-7 , 0 , 0\right)$ along the x-axis? Does the answer change if the path of the test charge between the same points is not along the x-axis?