Помогите с дз плиз

Первая бригада может выполнить задание за 16 часов, а вторая – за 48 часов. За сколько часов обе бригады выполнят задание при совместной работе?

Через первую трубу бак наполняется за 30 минут, а через вторую – за 40 минут. За сколько минут наполнится бак через обе эти трубы? 

Упр. 202. В следующих предложениях измените время глагола на Present Perfect. Переведите предложения на русский язык.

1. I am eating my breakfast.

2. We are drinking water.

3. He is bringing them some meat and vegetables.

4. You are putting the dishes on the table.

5. They are having tea.

6. She is taking the dirty plates from the table.

7. The children are putting on their coats.

8. The pupils are writing a dictation.

9. My friend is helping me to solve a difficult problem.

10. I am learning a poem.

11. She is telling them an interesting story.

12. Kate is sweeping the floor.

13. The waiter is putting a bottle of lemonade in front of him.

14. Susan is making a new dress for her birthday party.

15. She is opening a box of chocolates.