yellow marked portion-1.33 from where it is came from?

Hey...I guess you are well aware of the Lens maker’s formula. It is given as,
1/f = (n_Lens/n_o – 1)(1/R1 – 1/R2)
In the question mentioned above, he has just taken the LCM, nothing else. The same thing can be written as
1/f = (1.5/1.33 – 1)(1/R1 – 1/R2)
Please recheck.