Bubbling thoughts 2

There are two soap bubbles with radii $R_1$ and $R_2$ . ( $R_1≠R_2$ )

Scenario A:- The two bubbles connect to each other, and the connecting interface is also spherical, with radius $R_a$ .

Scenario B:- The two bubbles coalesce to form a single bubble, with a radius $R_b$ .

Find $R_a + R_b$ (in centimeters)

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Details : $R_1=4cm$ and $R_2=3cm$