Write SQL query to solve given problem: Among the parts that are returned, how many of them are provided by a supplier in debt?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT COUNT(T1.l_partkey) FROM lineitem AS T1 INNER JOIN supplier AS T2 ON T1.l_suppkey = T2.s_suppkey WHERE T1.l_returnflag = 'R' AND T2.s_acctbal < 0