LOst my Class Lock

today when i go to school , i see my class lock was disappear . yesterday i remember i took to a teacher which is lend my class to teach their class EST( English for Science and Techlonog) i ask the teacher to help me to lock after their finish class because i need to go home early yesterday. Now the lock disappear and i need to find it out. after this thing happen , i think i never will lend my class to any people already.