Old puddle raised problem for marsupial (7)
I believe the answer is:
opossum
'for marsupial' is the definition.
(opossum is a kind of marsupial)
'old puddle raised problem' is the wordplay.
'old' becomes 'o' (abbreviation).
'puddle' becomes 'sop' (I can't explain this - if you can you should believe this answer much more).
'raised' is a reversal indicator (going up in a down clue).
'problem' becomes 'sum' (arithmetic problem).
'sop' backwards is 'pos'.
'o'+'pos'+'sum'='OPOSSUM'
Can you help me to learn more?
(Other definitions for opossum that I've seen before include "Small arboreal marsupial" , "American native" , "American marsupial with prehensile tail" , "American arboreal marsupial" , "Thick-furred marsupial of the Americas" .)