1. I will finish my homework by 3 o'clock.
2. I will have finished my homework by 3 o'clock
3. I will finish my homework at 3 o'clock.
My question here is what I can answer my students if they ask
how the future tense and future perfect are different.
Is sentence 1 and 3 grammatical?
Will it be safe to say sentence 1 and 2 are interchangeable to my students?