<|system|>
Suppose that $x = 2+2t$ and $y = t - 21$.  If $x = 8$, what is $y$?</s>.
<|user|>
Can you answer based on context?
<|assistant|>
If $x=8$, then $8 = 2+2t$, so $2t = 6$ and $t = 3$.  Therefore, $y = 3 - 21 = -18.$