Using the notation $($Ai$,($Bm$,$ Bn$))$ for the strategy profile, where $Ai$ is $A^{\text{'}}$ s strategy and $(Bm,Bn)$ is $B^{\text{'}}s$ strategy, where $Bm$ is the move to follow after $A1,$ and $Bn$ is the move to follow after A$2,$ answer:

The subgame perfect Nash equilibrium $($SPNE$)$ of this game is $$

There are potentially up to two other Nash equilibria in this game that are not SPNE: If existent, the Nash equilibrium that returns the same payoff as the SPNE is:

The Nash equilibrium that returns a different payoff is $$