Under isothermal conditionss, two soap bubbles of radii a and b coalesce to form a single bubble of radius c. If the external pressure is P, then surface tension of the bubbles is

Options

A. `(P(c^3-a^3+b^3))/(4(a^2+b^2-c^2))`
B. `(P(c^3-a^3-b^3))/(4(a^2+b^2-c^2))`
C. `(P(c^2+a^2-b^2))/(4(a^3+b^3-c^3))`
D. `(P(c^3+a^3-b^3))/(4(a^2+b^2-c^2))`