1/3(21-3a)=6-a
I simplified the equation to the form, which is simple to understand
1/3(21-3a)=6-a
Simplifying:
+ 0.333333333333*(21-3a)=6-a
Reorder the terms in parentheses
+(+7-1a)=6-a
Remove unnecessary parentheses
+7-1a=+6-a
We move all terms containing a to the left and all other terms to the right.
-1a+1a=+6-7
We simplify left and right side of the equation.
a=-1
0=-1
The left and right sides are not equal, therefore there is no solution. This equation is invalid
Hope this helped