Below is a schedule of operations for two transactions that are executed within a database system. (a) Explain the problem that will occur if transaction A fails and (b) describe a concurrency control technique that a DBMS should implement to avoid this problem. Transaction A read_item(X); X:= X-N; write_item(X); read_item(Y); Transaction B read_item(X); X:=X+M: write_item(X);