At every table there is a really good working computer.
good is an adjective
adjectives are modified by adverbs
really is an adverb (real is an adjective)
It would be possible to say the following, but I don't think it's what you mean:
At every table there is a real, good, working computer.
The above means something like:
At every table there is a good working computer that is real (not imaginary or fake).
Finally, you sometimes hear even native speakers of English say that something is "real good", but this is not standard (or "correct") English and I would not recommend its use in an exam. Adjectives are modified by adverbs.