Mashaal Masha
In the system of equations below, $a$ and $c$ are constants.

$$\frac{1}{2}x+\frac{1}{3}y=\frac{1}{6} \\ ax+y=c$$

If the system of equations has an infinite number of solutions $(x,y)$, what is the value of $a$?
Difficulty: Hard
A: 

$-\dfrac{1}{2}$

B: 

$0$

C: 

$\dfrac{1}{2}$

D: 

$-\dfrac{3}{2}$

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