Hey there!
So, if [tex]y=(4)[/tex], this would mean that we would do [tex](2 \ * \ 4)[/tex] and from this, we would get 8.
We will then need to find what is [tex](x)[/tex].
[tex](x) = 7[/tex]
[tex]8*7[/tex] = [tex]\boxed{56}[/tex]
So, the equation would really look like . . .
[tex] \left[\begin{array}{ccc} 8*(7)-2*4 = 48 \\ \\ x=\boxed{7}\end{array}\right] [/tex]
Hope this helps.
~Jurgen