(−23x)+(−813x)= (-\frac{2}{3}x)+(-8\frac{1}{3}x)= (−32x)+(−831x)=
Let's remember the rule:
+(−x)=−x +(-x)=-x +(−x)=−x
Now let's write the exercise in the appropriate form and solve it:
−23x−813x=−9x -\frac{2}{3}x-8\frac{1}{3}x=-9x −32x−831x=−9x
−9x -9x −9x