#1) subtract x from both sides
[tex]a \: \: \: \: = \: \: \: \: \: \: \: \:zv + x \\ - x \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: - x[/tex]
you end up with
[tex]a - x = zv[/tex]
#2) divide by z
[tex] \frac{a - x}{z} = \frac{vz}{z} [/tex]
you end up with
[tex]\frac{a - x}{z} = v[/tex]
