The second line of Balmer series has wavelength 4861 Ao The wavelength of the first line of Balmer series is

For  first member,1λ1=R122−132or   1λ1=R14−19or  1λ1=R9−436or     λ1=365RFor second member1λ2=R122−142  or  1λ2=R14−116or  1λ2=R4−116  or 1λ2=3R16or  λ2=163RNow,  λ1λ2=365R×3R16  or  λ1λ2=2720or   λ1=2720×λ2=2720×4861 Ao=6562.4 Ao