Step-by-step explanation:
12 - 1/2r = ( 13 - 3/2r ) - ( 1 - r )
r - 13/6 = ( 7r - 3/2 ) - ( 2/3 + 6r )
13r + 20 = ( 6r + 7 ) + ( 13 + 7r )
-12 + r = ( -8 - r ) + ( 2r - 4 )
