[Grammar] Phrasal Verbs

Hi! I have a question related to a doubt that came up today when I got my English test on Phrasal Verbs.

So, the following sentence was involved:

'He returned the money to the man who had lost it.'

And I had to replace the verb 'returned' with 'give back'. So I wrote:

'He gave back the money to the man who had lost it.'

After I got the test and noticed that the teacher marked my answer as wrong, I understood it was correct to say 'gave the money back' instead of what I wrote. But then, a similar case came up, on a sentence whose answer was something like 'the firemen put out the fire' - and a friend of mine said 'put the fire out'. Then, I related it to my own mistake. Except this time, my teacher said her answer was correct. Now, that didn't sound right to me.
I googled it, and 'gave back the money', as well as 'gave the money back' seem to be correct, because it appears to be an optionally separable phrasal verb.
Can anyone help me?

[abaka]

I would agree with you: both forms are common. Except that:

"He gave back the money to the man who had lost it" is casual and loose.

"He gave the money back to the man who had lost it" is more precise English, because the money is handed "back to the man" who had lost it.

[Tdol]

It is optionally separable and, unlike Abaka, I don't see one form as more precise than the other.