Why is my internet conection slow on only one computer?

All my devices in the house run really well on the wifi but one computer (the farthest) has Really bad wifi. I cannot deal with it and its been going on for a while. I have 3 bars usaully for the wifi but it is still slow. I am trying to get a ethernet cable in this room see if that helps but is there anything i can do to fix it? Maybe I set my max bandwith to something without me knowing? Please help! Anything is helpful! BTW I have tried to restart my router many times, including a factory reset!

Slow Computer Speed Test Results: Ping (5) Download Speed (3.35) Upload Speed (0.16)
My IPHONE from the same room as my slow computer results: Ping (4) Download Speed (18.79) Upload Speed (6.85)

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