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