Can someone explain to me why these answers are incorrect? then explain the correct the answer?

They are incorrect because they add an extra word to them plus it would not sound right if it said I worked on my homework since of 5 in this case you would take out "of" same with spanish you would not add " hace" into the sentence

desde hace basically is a 2 word you add to when it's past tense

Question 2: Hago la tarea las cinco.

Answer 2: Hago la tarea desde las cinco.

Translation 2: I do the homework since five o'clock.

Question 3: Ellos reciclan las tres.

Answer 3: Ellos reciclan desde las tres.

Translation 3: They recycle since three o'clock.

Question 4: Nosotros bailamos cinco minutos.

Answer 4: Nosotros bailamos desde hace cinco minutos.

Translation 4: We have been dancing for five minutes.

Question 5: Mi madre cocina las diez de la mañana.

Answer 5: Mi madre cocina desde las diez de la mañana.

Translation 5: My mother cooks since ten in the morning.  

c is the correct answer for this question.