Let `bar(a)=-bar(i)-bar(k)`, `bar(b)=-bar(i)+bar(j)` and `bar(c)=bar(i)+2bar(j)+3bar(k)` be three given vectors. If `bar(r)` is a vector such that `bar(r)timesbar(b)=bar(c)timesbar(b)` and `bar(r)*bar(a)=0`, than `bar(r)*bar(b)`=