1. Let's understand why we write $2z$ and $2y$ in algebra. 2. When you see $2z$, it means $2 \times z$, which is the number 2 multiplied by the variable $z$. 3. Similarly, $2y$ means $2 \times y$, the number 2 multiplied by the variable $y$. 4. This is a shorthand notation: writing $2z$ instead of $2 \times z$ makes expressions simpler and easier to read. 5. Important rule: when a number is directly next to a variable, it means multiplication. 6. For example, if $z=3$, then $2z = 2 \times 3 = 6$. 7. Likewise, if $y=5$, then $2y = 2 \times 5 = 10$. 8. So, $2z$ and $2y$ represent twice the value of $z$ and $y$ respectively. 9. This is a fundamental concept in algebra to combine numbers and variables efficiently.