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Both are incomplete without each other and pose a different set of challenges when working with. Tbh the question is silly. And please search before posting. This might be a duplicate question.
both are used for diffrent things front-end is what the user sees the backend is databases among other things
They are the same if you look at importance. The Front end is nothing without a back end and a back end is nothing without a front end. Please use the search bar this question has been asked before. https://www.sololearn.com/Discuss/2412082/is-frontend-developer-important-like-backend https://www.sololearn.com/Discuss/2275709/frontend-vs-backend-which-one-is-better-learning-for-the-future
They are complementary. Front-End is used to manage the (Front) side which interacts with the user in the "higher" part of the Application Back-End is used to manage, the (Back) side which interacts with databases, starting with, Sessions/Cookies, DB Queries, Behind Architectures, etc.. A very tiny (simple) Example : When you're registering to a website, you interact with the internal side through the front one. Then you press "register" for instance, an internal value (flag) will change its state by pressing it. A Back-End program is watching this last one until it changes. After the event, a frame is sent to the servers following the OSI standards containing, instructions/data and others flags. The database receives the frame then changes will happen in it, by adding a new account (storing data) with your coordinates. So without pressing the "button" which is the Front-End (Presentation) you're not able to register you're data in the DB (Back-End)