Measuring a distance between walls through one of the walls sounds like a tall order to me, if possible at all (and if so almost certainly way out of reach of a school project) so more details and sketch of the general setup are in order.
Measuring a distance between walls through one of the walls sounds like a tall order to me, if possible at all (and if so almost certainly way out of reach of a school project) so more details and sketch of the general setup are in order.