SOLUTION: Can you please help me. I'm want to solve this system of equation using the substitution method. -3x+3y=4 -x+y=3

-3x + 3y = 4,   (1)
-x  +  y = 3    (2)

From (2), express y = 3+x and substitute this expression into equation (1) replacing y. You will get

-3x + 3(3+x) = 4.

Simplify:

-3x + 9 + 3x = 4.

9 = 4.


Absurd ?  Sure.  It means that the original system has no solutions.
It is inconsistent. 


One can see it immediately/instantly after seeing the original system.
Indeed, multiply the second equation by 3. 
You will get an equivalent equation

-3x + 3y = 9.   (2')

Now compare (2') with (1). They have identical left sides, but different right sides.
Such a system is inconsistent.