Final answer:
Javier can solve the problem of low wireless internet speed in his office by using a Wi-Fi extender, which amplifies and rebroadcasts the router's signal to extend coverage.
Step-by-step explanation:
To address the issue of low wireless internet speed at the back of a large office space, Javier can use a Wi-Fi extender. A Wi-Fi extender, also known as a range extender, is a type of wireless repeater used to expand the reach of a wireless LAN. The device is situated between a base router or access point and a client that is not close enough to receive acceptable service or one that is on the opposite side of a barrier. The extender connects wirelessly to the router, amplifying and rebroadcasting its signal into new areas of the office, which can significantly improve the wireless coverage and performance.