Two soap bubbles of radii x and y coalesce to constitute a bubble of radius z. Then z is equal to

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

Two soap bubbles of radii r and 2r are connected by a capillary tube-value arrangement as shown in the diagram. The value is now opened. Then which one of the following will result

When two soap bubbles of radii r_1 and r_2 (r_2 > r_1) are in contact, the radius of curvature of common surface is