Puzzle of the week #332

Irving Chernev was a chess player and prolific chess author. His expression "Every chess master was once a beginner" is as famous as his books and it proves to be right time and time again. In this game Magnus Carlsen (black) was only 11 years old at the time and with his last move (Ra8-c8) he wanted to exchange all the Rooks for an easier to play endgame. Unfortunately this was a costly mistake. Your tasks:
a) Who was better in this position and why?
b) How did white win the game here?
Total available points for this puzzle is 20. The answers will be published next time together with puzzle #333.

Puzzle #331 solution:
Game Pressl – Trtanj, World Seniors 2013. This week's best answers are by Jacey for question (a) and the top point scorers for question (b):
"a) The middle game begins when each side has developed all or most of their pieces, and when both Kings are in safe spots, aka castled"
[Event "Puzzle #331"][Date "2018.01.14"][Result "1-0"][SetUp "1"][FEN "r3r1k1/p2b1pp1/3qpnp1/3pN3/1p1P1P2/2P4R/PP1N2PP/R2Q2K1 w - - 0 1"]1. Rh8+ Kxh8 2. Nxf7+ Kg8 3. Nxd6

Correct solutions:
Matthew, Lyvia, Glyn - 10 points
Joey - 9 points
Eric - 7 points
Jacey, Coby - 6 points
Mengbai, Brian - 5 points
Lucas, Zhengyu, Darius, Chris - 2 points