For what value of the constant $a$ does the system of equations below have infinitely many solutions?  \begin{align*} 2x + 5y &= -8,\\ 6x &= 16 + a - 15y \end{align*}
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For what value of the constant $a$ does the system of equations below have infinitely many solutions?  \begin{align*} 2x + 5y &= -8,\\ 6x &= 16 + a - 15y \end{align*}
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For what value of the constant $a$ does the system of equations below have infinitely many solutions?  \begin{align*} 2x + 5y &= -8,\\ 6x &= 16 + a - 15y \end{align*}
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