こわれる/われる　＆　ある/おく

われる/われる ＆ ある/おく
1) What is the different between こわれる and われる？ Is われる more like shatter (for glass and the like)? And こわれる is for things like phone, car, computer which don't shatter?
2)My book says that a verb in -te form plus aru is used when something has been done for a specific purpose or with intention.
And a verb in -te form plus oku is used when something is done/prepared for future convenience. So, why does it claim that あります is the correct choice in the following:
a: 今度の会議についての確認ですが、会議室はもうよやく してあります.
b: はい。 もう予約してあります。
(Isn't making a reservation quite clearly something one does for future convenience?)
Thanks in advance.

1)
Those two verbs are overlapping in some cases. 割れる has a nuance of "to break into two or three pieces" or "to crack", but can also mean "to shatter" when used with, for instance, 粉々に. 壊れる is more close "to shatter", and hardly used for "to crack".

電話/車/コンピューターが壊れる usually means "to break down/not to work".

2)
今度の会議についての確認ですが、会議室はもうよやく してありますか？

予約しておきます means "I will make the reservation", thus, the reservation is not made yet. So, b can answer 予約しておきました instead of 予約してあります, whereas ある can't use when the answer is "No, not yet. I'll do it by tomorrow".