I will have to eat: 먹어야 할 거에요/먹어야 될 거에요 I had to eat: 먹어야 했어요 I have to eat: 먹어야 해요/먹어야 돼요 I'm not sure of '먹어야 됐어요' for I had to eat. It doesn't sound so natural to me.

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