The given equation is:
⇒
+ 4x – 3x – 12 = 0
⇒ x(x + 4) – 3(x + 4) = 0
⇒ (x – 3)(x + 4) = 0
⇒ x – 3 = 0 or x + 4 = 0
⇒ x = 3 or x = -4
therefore, the solution set of the given equation can be written in roaster form as {3, -4}
So, J = {3, -4}