Nonlinear equations in one variable and systems of equations in two variables SAT question

The correct answer is $9$. The given equation can be rewritten as $5|4-x|=25$. Dividing each side of this equation by $5$ yields $|4-x|=5$. By the definition of absolute value, if $|4-x|=5$, then $4-x=5$ or $4-x=-5$. Subtracting $4$ from each side of the equation $4-x=5$ yields $-x=1$. Dividing each side of this equation by $-1$ yields $x=-1$. Similarly, subtracting $4$ from each side of the equation $4-x=-5$ yields $-x=-9$. Dividing each side of this equation by $-1$ yields $x=9$. Therefore, since the two solutions to the given equation are $-1$ and $9$, the positive solution to the given equation is $9$.