If X+Y = 2X-2Z, X-2Y = 4Z and X+Y+Z = 21, what is the value of Z/Y?  Choose the correct choice from the following choices:
A) -4.5.
B) -2.
C) -0.5.
D) 3.
E) 2.5.
X+Y = 2X-2Z   X-Y = 2Z---------- 1   X-2Y = 4Z--------- 2   Subtracting equation 1 from equation 2   2Z = -Y   Z/Y= -0.5   -0.5. is the answer
<result>C</result>
If X+Y = 2X-2Z, X-2Y = 4Z and X+Y+Z = 21, what is the value of Z/Y?