1 cong viec neu 2 nguoi cung lam thi sau 9 gio se hoan thanh.Luc dau 2 nguoi cung lam trong 5 gio thi nguoi thu nhat nghicon nguoi thu hai lam tiep 3 gio nua thi con 1 phan nam cong viec nua chua lam.Hoi neu lam rieng thi moi nguoi can bao lau de hoan thanh cong viec do?