if the verb stem is ended with --ㅂ,there will be some special changes when it's followed with vowel.
the steps are 1: delete 'ㅂ' ; 2:add a' 우' 3:add the vowel
eg: 맵다(verb stem 맵)+어요
2:add a 우:매--매우
3.add the vowel: 매우---매워요
and in this sentence,맵다+(으)ㄴ 가요(interrogative ending)?-----매운가요?