four solutions:let the 9 nos are a(0),...,a(8) such that a(k)=a(0)+kd(1)-4=a(4),1=a(5),6=a(6) (3)-4=a(6),1=a(5),6=a(4)gives d=5,a(0)=-19 gives d=-5,a(0)=21-4 -9 16 -4 21 -1421 1 -19 -9 1 11-14 11 6 16...