как получить P2O5 из PH3?

Сколько воды надо добавить к 600г жидкости, содержащей 40% соли, чтобы получился 12%-ный раствор этой соли?

Написать миниатюрное сочинение (5-6 предложений хватит) на тему Какой я увидел зарубежную литературу на рубужу 19-20 веков.

. They (to have) tea when I (to come) home. 2. He (to walk) along the river when a boat (to pass). 3. We (to listen) to an interesting lecture on UFOs yesterday. 4. When I (to enter) the classroom, the teacher (to write) words on the blackboard and the pupils (to copy) them into their exercise-books. 5. They (to get) ready to go out when it (to begin) raining. 6. Yesterday at one o’clock I (to have) lunch. 7. When he (to come) in, I (to do) my exercises. 8. What you (to do) at eight o’clock yesterday? 9. At this time yesterday I (to ride) home by my bicycle. 10. You (to sleep) when I (to go) out. 11. I (to walk) along the street with my friend when a tram (to pass). 12. We (to discuss) our plans for the weekend when Nick (to rush) into the room. 13. I (to copy) files from my flesh-card when suddenly the computer (to hang). 14. Yesterday my sister (to celebrate) her birthday. The telephone (to ring) the whole day. 15. The doctor (to examine) the patient the whole week but (not to find) the cause of his pains.

Поверхность пруда постепенно закрывается вырастающими в нем кувшинками. Кувшинки растут быстро, что за каждый день закрываемая ими площадь удваивается. вся поверхность пруда закрылась за 30 дней. За сколько дней была закрыта первая половина всей поверхности пруда?