What is the difference between eolma and myeoch=how much
Eolma-i kabangi eolmayeyo?
Myeoch-myeoch sie mannalkkayo?
Both of them have the same meaning, how much, haven't they?
When I can use eolma and when I can use myeoch?
Thank you.

Question

What is the difference between eolma and myeoch=how much
Eolma-i kabangi eolmayeyo?
Myeoch-myeoch sie mannalkkayo?
Both of them have the same meaning, how much, haven't they?
When I can use eolma and when I can use myeoch?
Thank you.

Answer

when you use noun for count(명, 개, 살, 마리 etc) you have to use 몇(myeot) 

you should use 얼마(eolma) when you expect to get an answer (VERY many, large, small, little etc).

 so in your example,
 이 가방은 얼마예요? i kabangen eolmayeyo,
 이 가방은 몇만원인가요? i kabangen myeot manwon ingayo? (만원 --> 10000 won)

 몇 시에 만날까요?
 myeoch sie mannalkkayo? 
 there is '시' so you can't use '얼마'