If invoice numbers are in sequence then following queries will do the job:

 DELETE FROM acc_trans WHERE trans_id IN (SELECT id FROM ar WHERE invnumber BETWEEN 'A-0001' AND 'A-0999');

 DELETE FROM invoice WHERE trans_id IN (SELECT id FROM ar WHERE invnumber BETWEEN 'A-0001' AND 'A-0999');

 DELETE FROM inventory WHERE trans_id IN (SELECT id FROM ar WHERE invnumber BETWEEN 'A-0001' AND 'A-0999');

 DELETE FROM dpt_trans WHERE trans_id IN (SELECT id FROM ar WHERE invnumber BETWEEN 'A-0001' AND 'A-0999');

 DELETE FROM ar WHERE invnumber BETWEEN 'A-0001' AND 'A-0999';