What is the value of $x$ if \begin{align*}x &= y+5,\\
y &= z+10,\\
z &= w+20,\\
\text{and }\qquad w &= 80?
\end{align*}
I know that $w = 80$, so I can plug that into the equation for $z$ and get $z = 80+20 = 100$. Now that I know $z = 100$, I can plug that into the equation for $y$ and get $y = 100+10 = 110$. Finally, now that I know $y = 110$, I can plug that into the equation for $x$ and get $x = 110+5 = 115$. So the value of $x$ is 115. 