Does the avg (arith. mean) of a, b, c equal c?

1. c-a = c+b

2. c=0

my answer is 1.

book answer is 3 1 and 2 are sufficent.


my approach

from 1, a+b = 0

mean a+b+c/3 = 0+c/3

since c/3 cannot be equal to c i thought 1 is sufficent.