How do I find the values of b and y?[A][b = [3 y] 4]

You are going to format that better, aren't you?

 

And what is A?

 

That's a lot like asking: "What is Ax= 4?" without telling us what A is. The only possible answer is "x= 4/A" or "X= A^-14".

The only possible answer to your question is
[tex]\left[\begin{array}{c} b \\ y \end{array}\right]= A^{-1}\left[\begin{array}{c} 3 \\ 4\end{array}\right][/tex]
until we know what "A" is.

Of course, if the problem really was what you said, that may be the correct answer!