Answer
The error is $4x$ and the correct answer is $x=4$.
Work Step by Step
The given system of equations is
$5x-7y=16$ ...... (1)
$x+7y=8$ ...... (2)
Add equation (1) and (2).
$\Rightarrow 5x-7y+x+7y=16+8$
Add like terms.
$\Rightarrow 6x=24$
Divide each side by $6$.
$\Rightarrow \frac{6x}{6}=\frac{24}{6}$
Simplify.
$\Rightarrow x=4$
Hence, the error is $4x$ and the correct answer is $x=4$.
