you can solve this in less than 3 minutes


What about cxb2 instead of axb2, you cannot pin a pawn anymore.
If 1. Rg7 cxb2 (avoiding your mate in 3) 2. Rb7 b1=Q+ (only move) 3. Rxb1+ axb1=Q+ 4. Qxb1#
The silent move 1. Rf2 cxb2 OR axb2 2. Rf1+ b1=Q (forced) 3. Rxb1+ axb1=Q+ 4. Qxb1#
Will also give the same result, but there is less to calculate.


no. because the black pawn in h2 will take your rook.