"Do you like my brother?"
Translation:Dych chi'n hoffi fy mrawd i?
The notes for this section explain this. There is a table there showing the full set of mutations - soft, nasal and aspirate - which letters they each apply to, and what the changes are.
The possessive fy is followed by a nasal mutation. In this example b- mutates to m-:
- brawd, fy mrawd - brother, my brother