The "2z" and the "z" are like terms. That means, they can be simplified into only one term.
2z has a coefficient of 2.
z has an implied coefficient of 1.
You can combine the two terms to z. Think of it this way:
Reorder the equation, but keep the value the same. Switch the "-4" and the "-z". So, you have
2z - z - 4 = 4
Now factor out a "z" from the first two terms.
z (2 - 1) - 4 = 4
Simplify the (2 - 1) to 3.
3z - 4 = 4
Add 4 to both sides.
3z - 4 + 4 = 4 + 4
"- 4 + 4" simplifies to 0, and "4 + 4" simplifies to 8.
3z = 8
Now divide both sides by 3.
3z / 3 = 8 / 3
"3z / 3" The 3's cancel out, so you're left with just z. "8 / 3" cannot be simplified any more.
So your final answer is: z = 8 / 3 or in decimal form z = 2.6667
