7(3-x)-3(7-x)=3(x-7)-7(x-3)

Solution for 7(3-x)-3(7-x)=3(x-7)-7(x-3) equation:

7(3-x)-3(7-x)=3(x-7)-7(x-3)

We simplify the equation to the form, which is simple to understand 
7(3-x)-3(7-x)=3(x-7)-7(x-3)

Reorder the terms in parentheses
+(+21-7x)-3*(7-x)=3*(x-7)-7*(x-3)

Remove unnecessary parentheses
+21-7x-3+*(+7-x+)=+3+*(+x-7+)-7+*(+x-3+)

Reorder the terms in parentheses
+21-7x+(-21+3x)=3*(x-7)-7*(x-3)

Remove unnecessary parentheses
+21-7x-21+3x=+3+*(+x-7+)-7+*(+x-3+)

Reorder the terms in parentheses
+21-7x-21+3x=+(+3x-21)-7*(x-3)

Remove unnecessary parentheses
+21-7x-21+3x=+3x-21-7+*(+x-3+)

Reorder the terms in parentheses
+21-7x-21+3x=+3x-21+(-7x+21)

Remove unnecessary parentheses
+21-7x-21+3x=+3x-21-7x+21

We move all terms containing x to the left and all other terms to the right. 
-7x+3x-3x+7x=-21+21-21+21

We simplify left and right side of the equation. 
0x=0

0=0

This equation is an identity, so all real numbers are solutions.