The work done in increasing the size of a soap film from $10 \mathrm{~cm} \times 6 \mathrm{~cm}$ to $10 \mathrm{~cm} \times 11 \mathrm{~cm}$ is $3 \times 10^{-4} J$. The surface tension of the film is $\quad$ [MP PET 1999; MP PMT 2000; AIIMS 2000; JIPMER 2001, 02]
(a) $1.5 \times 10^{-2} \mathrm{Nm}^{-1}$
(b) $3.0 \times 10^{-2} \mathrm{Nm}^{-1}$
(c) $6.0 \times 10^{-2} \mathrm{Nm}^{-1}$
(d) $11.0 \times 10^{-2} \mathrm{Nm}^{-1}$