The answer is 0 and here is why.
Put each variable in terms of X. So
y=(c-a)x/(b-c) and
z=(a-b)x/(b-c)
now the sum of x,y,z becomes
x+ (cx-ax)/(b-c) + (ax-bx)/(b-c)
now put everything in terms of the common denominator (b-c) and we get
[(bx-cx)+(cx-ax)+(ax-bx)]/(b-c)
now you can see that each term in the numerator cancels out so we have 0! And 0/ anything(except 0) is 0