The matrices
\[\begin{pmatrix} 2 & a \\ -3 & -1 \end{pmatrix} \quad \text{and} \quad \begin{pmatrix} -\frac{1}{16} & b \\ \frac{3}{16} & \frac{1}{8} \end{pmatrix}\]are inverses.  Enter the ordered pair $(a,b).$
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
The matrices
\[\begin{pmatrix} 2 & a \\ -3 & -1 \end{pmatrix} \quad \text{and} \quad \begin{pmatrix} -\frac{1}{16} & b \\ \frac{3}{16} & \frac{1}{8} \end{pmatrix}\]are inverses.  Enter the ordered pair $(a,b).$
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
\left( 6, -\frac{3}{8} \right)
The matrices
\[\begin{pmatrix} 2 & a \\ -3 & -1 \end{pmatrix} \quad \text{and} \quad \begin{pmatrix} -\frac{1}{16} & b \\ \frac{3}{16} & \frac{1}{8} \end{pmatrix}\]are inverses.  Enter the ordered pair $(a,b).$
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