Answer:
Star B is hotter than star A.
Explanation:
A main-sequence star of spectral type F2 has an average temperature of 6000K - 7500K.
A white dwarf B4, is essentially a dying star, and in its final stage of life, the star will start to cool down slowly, however, this process is terribly slow and during they lifetime, they have an average temperature of around 10.000 K - 30.000 K. Thus, Star B is much hotter than star A.
