The line between qc and qb is not necessary for now. The question wants the attractive force between qb and qa, which is an arrow facing upwards from qb .
The attractive force between qb and qc is an arrow facing outward from qb to qc. check my diagram from Rathebe"s answer.
The attractive force between qb and qc is an arrow facing outward from qb to qc. check my diagram from Rathebe"s answer.