So the I3=(Vc+9-Vb)/1 ?You know what, none of your two solutions is correct. Why? Because you made the same error in your hand calculation and in LTspice. In simply words your "definition" of an I3 (and Vx voltage) current is wrong.
How can I3 be equal to I3 = (Vc - 9V) /1Ω?
Do you see the error?
Yes, this is incorrect.this is incorrect I3=(Vc+9-Vb)/1 (?)
No, you cannot do that. In this case, this is incorrect. Because of the fact that the "control voltage" (Vx) is not equal to Vc - VbI draw again the circuit making source transformation and help me.
The dependent source absorbs power from the circuit (2.522 W)What did you get for a final result?