[tex]\\ \sf\longmapsto \dfrac{-1}{3}+(\dfrac{-3}{8})[/tex]
[tex]\\ \sf\longmapsto \dfrac{-8+(-9)}{24}[/tex]
[tex]\\ \sf\longmapsto \dfrac{-8-9}{24}[/tex]
[tex]\\ \sf\longmapsto \dfrac{-17}{24}[/tex]
-1/3 + -3/8
denominator: -1/3 * 8
-3/8 * 3
<=> -8/24 + - 9/24
<=> (-8 + -9)/24
= -17/24