How can white mate black in 4 moves in this particular game. How can white mte black in 4 moves in this game. This might be easy but I am a beginner.
(https://i.stack.imgur.com/r5n6R.png)
The king has no escape squares and, as is often the case in these puzzles, every move must be a check.



[FEN "r1br4/1p3qp1/p1kb3p/2NN1p2/1PPQ4/8/P5PP/R4RK1 w - - 0 1"]

1. b5+ axb5 2. cxb5+ Kxb5 3. Rfb1+ Kc6 4. Rb6#