Respuesta :
Its 12y - 9 because when u add twelve pluus 12 it 24 then -21 is to 3 which 12 - 9 is 3
Use the commutative property..
(12y - 21y) + 12 =
-9y + 12 =
-9y = -12
y = 12/9 = 4/3 = 1 1/3
(12y - 21y) + 12 =
-9y + 12 =
-9y = -12
y = 12/9 = 4/3 = 1 1/3