Why equilibrium potential vary with changes in concentration

Question

Problem

A. What is the Na⁺ equilibrium potential when? Na⁺ _out equals 100 mM and? Na⁺ _in equals 10 mM?

B. What is the Na⁺ equilibrium potential when??Na⁺ _out equals 100 mM and? Na⁺ _in equals 100 mM?

C. What is the K⁺ equilibrium potential when K⁺ _out equals 10 mM and K⁺ _in equals 100 mM?

D. Why does the equilibrium potential vary with changes in the concentration of these ions?