is that female flies have 6 + 2 or 8 legs,
and male flies have 6 ÷ 2 or 3 legs.
Note that an ordinary fly has six legs.

This chart shows some possible ages for Bertie, Ben, and Sue.

Experiment with possible ages, adding together:
    "double one brother, plus treble the other, plus Sue's age..."
    2x Bertie (or Ben) + 3x Ben (or Bertie) + Sue's age