We want to find if there exists an $x$ such that for all $y$, $P(x,y) = 0$.
If $y=0$, then $P(x,0) = 0$.
If $y=1$, then $P(x,1) = 3x^2 - 18x = 3x(x-6) = 0$, so $x=0$ or $x=6$.
If $y=2$, then $P(x,2) = 10x^2 - 44x - 48 = 0$, which gives $5x^2 - 22x - 24 = 0$.
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