Answer:
"Let me show you a trick that will save you some time and effort"
Step-by-step explanation:
Based on the scenario being described within the question it can be said that the most effective form of feedback would be by telling the coworker "Let me show you a trick that will save you some time and effort". This statement will help the co-worker increase his/her efficiency as well as increase self esteem and your bond as co-workers.