Isolate y in the first equation.
[tex]2y = 10x[/tex]
[tex]y = 5x[/tex]
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Then plug this into the second equation
[tex]\frac{x^2}{64}-\frac{y^2}{36} = 1[/tex]
[tex]\frac{x^2}{64}-\frac{(y)^2}{36} = 1[/tex]
[tex]\frac{x^2}{64}-\frac{(5x)^2}{36} = 1[/tex]
[tex]\frac{x^2}{64}-\frac{25x^2}{36} = 1[/tex]
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So the final answer is choice A
