Two soap bubbles of radii a and b combine to form a single bubble of radius c. If P is the external pressure, then the surface tension of the soap solution is

• A. \[\frac{P({{c}^{3}}+{{a}^{3}}+{{b}^{3}})}{4({{a}^{2}}+{{b}^{2}}-{{c}^{2}})}\]
• B. \[\frac{P({{c}^{3}}-{{a}^{3}}-{{b}^{3}})}{4({{a}^{2}}+{{b}^{2}}-{{c}^{2}})}\]
• C. \[P{{c}^{3}}-4{{a}^{2}}-4{{b}^{2}}\]
• D. \[P{{c}^{3}}-2{{a}^{2}}-3{{b}^{2}}\]