Maybe meters? I have a 35 foot HDMI cable so that's just over 10. I see 50 foot HDMI cables so that length is out there. Try to keep it on the shorter side.
As to coax, it is not usable due to differences in HDMI signaling and frequencies. Since that's a dead end, direct your efforts to a longer length HDMI cable. Here they don't cost much.
https://www.amazon.com/BlueRigger-High-Speed-Cable--wall/dp/B004GW25WY/ is about 25 bucks to my mailbox.
I wanted to connect my set top box having HDMI/AV slots to my flat screen TV having the same but the problem is with the cables being too short where as for this I need at least 10-15 mts. For which I want to extend by using another HDMI or AV male socket .The coaxial cables have more than 10 individual wires there fore kindly tell me how to join together the different wires. Thanks.