Solve for x.
4x-5/y=2z

So you don't know the value of x, y, or z; all you're told is to solve for x. This is not impossible (even though it may seem like it). Your answer will have several variables in it, but in algebra you won't always have the complete answer.
Start with the equation: 4x - 5 / y = 2z
The first thing you'll want to do to it is try to get x alone on one side.
4x - 5 / y = 2z
       +5       +5 --> 4x / y = 2z +5
                               *y           *y --> 4x = y (2z + 5)
                                                        /4              /4   --> x = (y (2z + 5)) / 4 
Your final answer will be: x = (y (2z +5)) / 4
Hope it makes sense to you!!