I couldn't solve it whatever I did

But draw is near. You want to win?

1. Ra3+ Kb4 2. Rab3+ Kc4 3. Rhd3 b1Q 4. Rxb1 Kxd3 and this looks like a draw

obvious draw........but coach said it is a win...

both pawns are stopped and will be taken by your king 

Matthew, 6. d8=Q?

still a draw

Obvious win

1.Rh5  Kb4  2.Rg3  Qb1/Qd1 3. Rh4+ followed by Rg5+ Rh6+ etc                 (unless Kc5 Rg5+ Qd5 Rxd5 Kxd5 Rb4.....)

I reached that far, now looking at a way to continue.

Oh lol, quite easy, Ra7+, King goes to somewhere, and then Rb8+ winning the queen, doubling rooks on the first rank, and white is winning.

ok, that looks convincing.  what about if Black goes to a4 instead of c4?

Asked about the initial position Stockfish DD says: "Tablebase: 1. Ra3+ White wins in 26 moves" (the last 14 of which are just K+R vs. K).

Yeah,oline TB also gives mate in 26

Here's one way:

simple.make your opponent resign by threatening them

Pretty sure post #10 nailed it.