If there are two charges q1 and q2 at separation R. If we introduce a metal sheet at midway perpendicular to the line joining them,what will be the new force experienced by any one of charge?

I think we can apply here, the concept of image charges. Just put a charge a -q1 with q2 so that there will be two charges q1 and (q2-q1) at a separation R. Now apply columb`s law.If the above method doesn`t work then apply the concept of induction.Please verify my former method.