4x=y

4x=y

What exactly is your question? If you need to solve your equation for x, then divide both sides by 4.

4x=y

Divide both sides of the equation by some quantity intended to isolate the "x". For example. Given the following equation, how can we make x the "subject"?

32x = 64y

If we divide both sides by 32, we'll get this:

\frac {\cancel{32}x}{\cancel {32}} = \frac { \cancel {64}^{2}\, y}{\cancel{32}}

x = 2y Viola!

divide by 4
x=y/4
I believe that there are much more difficult problems in which you have to make x the subject.