Mashaal Masha
$$y=2x^{2}-21x+64$$ $$y=3x+a$$

In the given system of equations, $a$ is a constant. The graphs of the equations in the given system intersect at exactly one point, $(x,y)$, in the $xy$-plane. What is the value of $x$?
Difficulty: Hard
A: 

$-8$

B: 

—6

C: 

$6$

D: 

$8$

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