How old is mother? What is the cost? (6)
I believe the answer is:
damage
'is the cost?' is the definition.
(I've seen this before)
'how old is mother?' is the wordplay.
I cannot quite understand how this works, but
'mother?' could be 'dam' (female parent of an animal) and 'dam' is located in the answer.
'how old' could be 'age' (I've seen this before) and 'age' is found in the answer.
No letters remain.
This explanation may well be incorrect...
'what' acts as a link.
Can you help me to learn more?
(Other definitions for damage that I've seen before include "Ravages" , "Impair, hurt" , "Cost (slang)" , "Physical harm" , "Harm, injury" .)