Eager in solving square root of 900 divided by s (7)
I believe the answer is:
thirsty
'eager' is the definition.
(thesaurus)
'solving square root of 900 divided by s' is the wordplay.
'solving square root of 900' becomes 'thirty'.
'divided by' is an insertion indicator.
'thirty' going around 's' is 'THIRSTY'.
'in' is the link.
(Other definitions for thirsty that I've seen before include "Needing a tipple" , "Needing moisture" , "Feeling dehydrated" , "Hungry" , "Feeling the need to drink" .)