This is the 337th most frequent Korean word.
얼마나
"얼마나" means "how much" or "how many" in English.
In this context, '얼마나' is used to ask about the degree of deliciousness.
이 케이크는 얼마나 맛있어요?
How delicious is this cake?
Here, '얼마나' is used to inquire the amount of time needed.
얼마나 걸릴까요?
How long will it take?
'얼마나' is used here to emphasize the extent of his hard work.