Among the suppliers for the parts ordered in order no.4, how many of them are in debt?
order no.4 refers to l_orderkey = 4; in debt refers to s_acctbal < 0
SELECT COUNT(T1.l_linenumber) FROM lineitem AS T1 INNER JOIN supplier AS T2 ON T1.l_suppkey = T2.s_suppkey WHERE T1.l_orderkey = 4 AND T2.s_acctbal < 0