'To the head teacher's office'

One way to obtain the Welsh equivalent of this type of English phrase is to:

• Put the English phrase the long way round:

  to the head teacher's office › i swyddfa'r pennaeth

• Get rid of the first 'the' and the 'of' in the phrase:

  to the office of the head teacher

  to office the head teacher › i swyddfa'r pennaeth

Remember that the preposition i causes a soft mutation. Also y and 'r will cause a soft mutation if they are followed by a feminine singular noun, e.g.

to the middle of the bridge > i ganol y bont