16 must be the answer. Both of the (0,0,0) & (1,0,1) will be mapped to either 0 or 1. Both of the (0,0,1) & (1,0,0) will be mapped to either 0 or 1. Both of the (0,1,0) & (1,1,1) will be mapped to either 0 or 1. Both of the (0,1,1) & (1,1,0) will be mapped to either 0 or 1. 4 pairs having 2 choices each, thus 4^2 = 16.