Use English for explanation let k be 9×109

Okay, Engineer, let's re-solve this problem using the specified value for $k$ and English explanations.

From the diagram and problem description:

• Side of the square, $a = 0.5 \, \text{m}$
• Charge at P, $Q_P = -22.2 \, \mu C = -22.2 \times 10^{-6} \, C$
• Charge at R, $Q_R = +44.4 \, \mu C = +44.4 \times 10^{-6} \, C$
• Coulomb's constant, $k = 9 \times 10^9 \, \text{N m}^2/\text{C}^2$ (as requested)

The distance from S to P ($r_{PS}$) is the side length of the square, so $r_{PS} = 0.5 \, \text{m}$.
The distance from S to R ($r_{RS}$) is also the side length of the square, so $r_{RS} = 0.5 \, \text{m}$.
The electric potential at S ($V_S$) is the sum of the potentials caused by charge $Q_P$ and $Q_R$.