"I have finished the worksheet."
Translation:Dw i wedi gorffen y daflen waith.
Why has gwaith become waith here? I presume it is a soft mutation, but the phrase is taflen gwaith when it stands alone,with no mutation of the second word. Is there a rule that, when a noun mutates, any further noun used in apposition to it mutates as well?
Adjectives (and nouns used as adjectives, as with gwaith here) undergo soft mutation when following feminine nouns. taflen is a feminine noun.
There is no occurance of 'taflen gwaith' in the course.
As already explained, taflen, is a feminine noun and a following adjective will mutate.