Router/Network Extender Issue

I just purchased a FIOS Gateway Router and a FIOS Network Extender and am having a problem with Wi-Fi signal strength. Currently my router is located in a bedroom at one end of the house because that's where the ethernet cable comes in to the house. (I have a single level ranch home...approx 2000 square feet.) I'm trying to set up a home office at the other end of the house where the network extender is located but the Wi-Fi signal in the office is very weak or non existent on both my phone and my computer.

Currently I use my laptop at a table in the middle of the house and the Wi-Fi signal strength is fine. There are currently 4 coax outlets in the house: #1 is the in the same bedroom as the router. #2 is in another bedroom on the other side of the wall from the router location. #3 is in the living room in the center of the house. #4 is in the home office at the other end of the house where the network extender is located.

Does anyone have any ideas/suggestions to increase the Wi-Fi signal strength in the home office? I can't move the router to the middle of the house because the ethernet cable isn't long enough. I could move the network extender to the middle of the house and connect it in the living room using a coax splitter.

Any suggestions would be greatly appreciated.