What criteria does this mixture have to satisfy to be separated by simple or fractional distillation

Hi, the given question is incomplete, the complete question is:

You carry out a reaction that yields a major product Q (boiling point: 120°C) and side product R (boiling point: 150°C). The ratio of Q to R is 70:30. Both Q and Rare liquids.

After the ethyl acetate is evaporated, Q and R (a mixture of liquids) remain. What criteria does this mixture have to satisfy to be separated by simple or fractional distillation (besides bp difference and composition)?

The basic criteria are that the two liquids should be miscible. A mixture of two miscible liquids is further separated by the process of simple distillation and fractional distillation. For the liquids that exhibit varied boiling points, with a difference of +30 degrees C, the process of simple distillation is used. On the other hand, for the liquids whose boiling points come between the range of o to 30 degrees C, the process of fractional distillation is used.

the answer is 0.42 is that is an option. this question provides no info