Explain the different interpretations possible from the following ambiguous statement: I can't tell you how much I enjoyed meeting your brother.
I can see at least 6 possible interpretations, but there are probably more:
1: The speaker is not allowed to tell the listener, but someone I else can. (I can't tell you...)
1a: The speaker isn't allowed to tell the listener, with no inference as to whether anyone else can.
2: The speaker is not allowed to tell the listener, but can tell someone else (I can't tell you...)
2b: The speaker is not allowed to tell the listener, with no inference as to whether the speaker can tell anyone else.
3: The speaker is not physically capable of explaining (I can't tell you...). This option does not make sense because if the speaker is capable of communicating their inability to explain, they should be able to explain how they felt.
4: The speaker is physically capable of explaining but cannot formulate the right words.
5: The speaker's emotions cannot be expressed in words, but only though other means (I can't tell you...)
6: The speaker is not sure how excited they were to meet the listener's brother and therefore can't tell the listener. (I can't tell you how excited...)
You can identify other interpretations by stressing different words in the sentence. Eg:
X: The speaker can tell the listener how excited they were to meeting everyone except the listener's brother (I can't tell... your brother)
The first and most reasonable interpretation would be "There are no words to describe my excitement of meeting your brother!", "I enjoyed meeting your brother so much I can't find the right words to tell you about it!"
One might think that the speaker really cannot tell how much they enjoyed the meeting, but this interpretation sounds wrong to me. Why can't they tell? Is it a secret?
So, the first is correct. By the way, Demis Roussos has a song called "Can't say how much I love you" and it goes like this:
I can't say how much I love you
Say how much I need you
I could never find the words to say
I really really want you and you are all my eyes can see
It's not that he really can't say how much he loves her. He can but there are no words to describe his love accurately. So, it's just a hyperbole, an exaggerated statement not meant to be taken literally.
I can't tell you how much I enjoyed meeting your brother.
This may seem ambiguous to the teacher who made the assignment. However, the speaker is telling the listener ('you') how much s/he enjoyed meeting his brother. He enjoyed meeting the brother. He says so. It's straightforward with no mystery. It's just idiomatic in certain respects.