Endgame position: The importance of tempos

In this post I would like to show an interesting position that occurred in one of my games. Before I show the postition however, i'd first like to point out a simpler version of the position that is always drawn even if one side manages to win a pawn.

Notice once again how in the mainline above, neither side win even if one of the pawns is lost. However, what happens if there are extra pawns on the opposite side of the board?

In the puzzle below, black has just played a6. What should whites follow up moves be?