Найти значение X . при котором значение дроби x+1  ___  x-3 больше значения дроби 7  _  X на 1

Почему гражданское общество в развитых странах сформировалось лишь в последние 2 столетия?

Сколько атомов и сколько молекул содержится в 2 моль Н2О?

Explain why it is so. (тема урока The Present Perfect Tense)

Объясни следующее. 

Example: - There are no pies on the plate. John (eat).
- John has eaten them.

1) - Their house is now yellow!
- Yes, they (paint) ... .
2) - He knows everything about Moscow.
- I think he does. He (be) ... there many times.
3) - John, your car looks so clean!
It should be! I (wash) ... .
4) - Your grandparents are tired.
Yes, they (come) back from the shops.
5) - Does Harry know about it?
- Yes, I (give) ... him a call.
6) - Is the book interesting?
- I don't know yet. I just (begin) ... reading it.
7) - Why is Jason in hospital?
- He (fall) ... off his bike.
8) - Roy knows nothing about our meeting.
- Sorry. I (not, speak) ... to him yet.