jmc

Substituting in $x=2$, we obtain the equations

$$\begin{array}{rl}y+6& =a,\\ 5y+4& =2a.\end{array}$$

Multiplying the first equation by $5$ and subtracting it from the second equation, we find

$$-26=-3a\Rightarrow a=\boxed{\frac{26}{3}}.$$