We have the equation
[tex]x=\frac{1}{2}(y+z)[/tex]And we have to solve it for y. The first step to do this is to get rid of the 2 that is dividing. To do that we should remember, if something is dividing we take to the other side multiplying. This is
[tex]2x=y+z[/tex]The second step to solve the equation is to get rid of the z, since it is adding we take it to the other side substracting. Then
[tex]y=2x-z[/tex]