c
Excess pressure inside the smaller soap bubble

\(\Delta {P}=\frac{4 {S}}{{r}_{1}}+\frac{4 {S}}{{r}_{2}}\ldots \text { (i) }\)

The excess pressure inside the equivalent soap bubble

\(\Delta {P}=\frac{4 {S}}{{R}_{{eq}}} \ldots \text { (ii) }\)

From \( (i) \,\& \,(ii)\)

\(\frac{4 {S}}{{R}_{{eq}}}=\frac{4 {S}}{{T}_{1}}+\frac{4 {S}}{{T}_{2}}\)

\(\frac{1}{{R}_{{eq}}}=\frac{1}{{T}_{1}}+\frac{1}{{I}_{2}}\)

\(=\frac{1}{6}+\frac{1}{3}\)

\({R}_{{eq}}=2 \,{cm}\)