You don't turn "degrees into feet and inches".
Center speaker is 0°.
Front LR is 15-20°
All speakers "should be" equal distance from the main listening position.
So...a 10x10 room(easy math) means you would be roughly 5.5 feet from every speaker if 7.1.
Go to 5.1 and you can slide rearward...
What is your overall budget?
Quiet Rock 500 or SoundBreak XP
You have no room for 7.1, unless your seating distance is 6 feet. Even a proper 5.1 is going to require no more than an 8ft seating distance.