Tìm x thuôc Z biết: (x+1) + (x+3) +(x+5)+...+(x+99)=0

tìm x thuôc Z biết
a, (x+1) + (x+3) +(x+5)+...+(x+99)=0
b,(x-3) +  (x-2) + (x-1)+...+10+11=11
c, x + (x+1) + (x+2) + ...+2018+2019=2019