The third conditional in this sentence, is correct?

In the following sentence transformation exercise:

"It was Sarah's ideas that enabled us to put on a successful fashion show."

Complete the following sentence so that it has a similar meaning to the first sentence, using the word given:

"FOR"

"If ____________________ ideas, we wouldn't have been able to put on a successful fashion show."

And the solution is: "it weren't for Sarah's"

I have two doubts:

1) That sentence is third conditional, isn' it? So it should be: (if + past perfect, ... would + have + past participle), why are they using Past Simple: it weren't for Sarah's ideas...

I would have written: If it hadn't been for Sarah's ideas, we wouldn't have been able to put...

2) Why "it weren't" and not "it wasn't"? The third person of the verb to be in past is "it was"

Thanks in advance,

Mónica

Separate or separated? which is the correct form in this sentence?

I would have written "To keep waste materials separated in three bins",  but I am not sure if it is correct, or I should write "To keep waste materials separate in three bins".

What is the correct form and why?

Thanks in advance,

Mónica

The use of 's

In the following sentence:

"Do you have any objection to Jonh's joining us for the meeting?"

Why do we have to add this apostrophe  ( 's ) to John? 

Thanks in advance,

Mónica

Another 24 hours

Is this correct? I would have written "OTHER 24 hours" because it is more than 1 hour, it is plural. However, I have seen this sentence:

"We have been working round the clock to solve this issue with your security system, but it's going to take us ANOTHER 24 hours to get it back online"

Thanks in advance,

Mónica

The use of "the"

Which of these sentences is correct? And why? I'm not sure when to use "THE" or not:

1) "Improvement in transport and global business are.."

2) "THE improvement in transport and global business are...."

3) "THE improvement in transport and THE global business are..."

Thanks in advance!

Mónica

Adjective + Noun

"Travelling by plane has become the safest and the best value for money " Is this sentence correct? I think that it need a noun after "safest",  because it is an adjective, for example:

"Travelling by plane has become the safest ALTERNATIVE and the best value for money".

Thanks in advance.

key or the key?