> Can anybody explain if i can use "that" instead of "so"?
In the sentences below, yes.
> if we can use, can you explain the resource grammar book expressing it?
No.
> Can you explain the issue on the following questions?
>
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>
> [What does "THAT" mean ?]
It roughly means "so". You could also use "too" or "very".
A similar construction is "as well as that", or "as well as all that", which
sound as if the "that" is referring to something else but really mean
something like "as well as might be expected".