All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, is His slave and Messenger.
Whoever dies and leaves behind one son and three daughters only and does not have any other heirs, then his inheritance should be divided by Ta’seeb (by virtue of having a paternal relation with the deceased and not having a fixed share, so they get what is left after the fixed shares have been distributed); the male gets twice the share of the female as Allah says (what means): {Allah instructs you concerning your children [i.e. their portions of inheritance]: for the male, what is equal to the share of two females.} [Quran 4:11]
Therefore, the inheritance should be divided into five shares; the son gets two shares, and each daughter gets one share.
Allah knows best.