$9x - 5x = x(9-5) = 4x$
$4x = 52$
3. $9x + (-5x) = 52$ (the + (-5x) would just be -5x.. positive times negative = negative) $9x - 5x = 52$ $4x = 52$ (subtracting like terms) $\frac {4x}{4} = \frac {52}{4}$ (isolating x by divinding by 4 on both sides) $x=13$