Beta Enterprise manufactures a product in two sequential departments. On $1$ September, Department Q had $2118$ units, which were $45$ per cent complete as to conversion cost. During September, $15899$ units were completed and transferred from Department P to Department Q$.$ On $30$ September, Department Q had $5173$ units, which were $25$ per cent complete as to conversion costs. Compute the number of units that were completed and transferred out from Department Q during the month of September.