If T is the surface tension of soap solution, the amount of work done is blowing a soap bubble from a diameter D to a diameter 2D is

Work done = (Increase in surface area) x Surface tension                 = 2×[4π(2D2)2-4π(D2)2]×T[Since, for sap bubble, there are 2 free surfaces]         = 2 × (4πD2-πD2)T = 6πD2T