20. Surface tension of a soap solution

is 1.9 x 10-2N/m . Work done in blowing a bubble of 2.0 cm diameter will be (a)  7.6 x 10-6  π  joule                      (b) 15.2 x 10-6 π joule (c) 1.9 x 10-6 π joule (d) 1 x 10-4 π joule …