An ellipse in the first quadrant is tangent to both the $x$-axis and $y$-axis.  One focus is at $(3,7)$ and the other focus is at $(d,7).$  Compute $d.$
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
An ellipse in the first quadrant is tangent to both the $x$-axis and $y$-axis.  One focus is at $(3,7)$ and the other focus is at $(d,7).$  Compute $d.$
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
\frac{49}{3}
An ellipse in the first quadrant is tangent to both the $x$-axis and $y$-axis.  One focus is at $(3,7)$ and the other focus is at $(d,7).$  Compute $d.$
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