Help white to win this:

EASY.

The only thing easy about that, Don3, was typing "EASY."

 i agree, curious puzzle

I hope this is little instructive, that you understand if you can achieve two neighbour pawns (phalanx?) on the 6th row, then rook can't stop both pawns from queening.

Its a mate in 13 puzzle, odd looking as it is =). I like it.

why couldnt black just play a8 queen.

chessbeast, look at the move list after completing the puzzle for the variations in which Black promotes the a2 pawn to a queen (on a1, not a8). It all ends up with White mating Black in the next few moves.

great sac