Puzzle of the week #320

Level: 
5-Queen
Chess Diagram: 

[Event "Puzzle #320"][Date "2017.05.29"][Result "1-0"][SetUp "1"][FEN "8/4kp2/4p1p1/2p1r3/PpP5/3R4/1P1K1PP1/8 w - - 0 1"]

Material is equal in this Rook and pawns endgame. Alekhine was still World Champion at the time of the game and here he proved why. You get to follow in his footsteps by doing the following tasks:
a) What is the main factor both sides have to consider in this endgame?
b) Using the main factor discovered at point "a", please show the best line ending the game you can think of

Total available points for this puzzle is 15. The answers will be published next time together with puzzle #321.

Puzzle #319 solution:
Game Borisenko - Gheller, Moscow 1950. The answers are:

[Event "Puzzle #319"][Date "2017.05.23"][Result "1-0"][SetUp "1"][FEN "2b2r1k/1p2Npbp/1n1Q2p1/1P6/1P3P2/1q4PP/5KB1/2R1R3 w - - 0 1"]1. Qxb6 ({The game move} 1. Nxc8) 1... Qb2+ 2. Kf1 Bd4 {White was afraid of the fact now Qb6 is under attack and in the same time black threatens Qb2-f2#} 3. Rc2! (3. Qxd4+ Qxd4 4. Nxc8 {Coco} (4. Rxc8? {Cody} 4... Rxc8 5. Nxc8 Qc4+ 6. Kg1 Qxc8)) 3... Qxb4 (3... Qxc2 4. Qxd4+ {Bradley} 4... f6 {Jalen}) 4. Nd5 Qa4 5. Qd6 Qxb5+ 6. Rce2

Correct solutions:
Jalen - 20 points
Bradley - 18 points
Coco, Cody - 15 points
Dheera, Deryk - 4 points
Benjamin - 3 points

Standings:
Jalen - 260 points
Coco - 227 points
Cody - 225 points
Bradley - 224 points
Benjamin - 130 point
Deryk - 111 points
Uros - 63 points
Dheera - 45 points
Yakov - 39 points

Comment: 

Limiting counterplay