Let `a=hat(i)+hat(j)+sqrt(2)hat(k),b=b_(1)hat(i)+b_(2)hat(j)+sqrt(2)hat(k)` and `c=5hat(i)+hat(j)+sqrt(2)hat(k)` be three vectors such that the projection vector of b on a is a. If `a+b` is perpendicular to c, then `|b|` is equal to