I am wondering if you noticed -겠-(끝마쳐야겠어요) and -(해)야-(끝마쳐야 해요/돼요) in each phrase.^^ "-겠-" indicates that someone is ready/willing to do sth or it's time to do sth. (*sth = something) For example, 그만 집에 가야 겠어요. = I'd better get going. = I should be going. = It's time to get going. 이젠 끝마쳐야 겠어요 = I should finish it. = I will finish it. = It's time to finish it. Whereas "-야-" is used to mean "need to do sth or have/has to do sth" so the second one will be "I need to finish it" or "I have to finish it" For instance, 나는 오늘까지 숙제을 끝마쳐야 해요 I need/have to finish my homework by today. = The homework needs/has to be done by today. ^______^