Who gets the win?

In high school, what does a pitcher have to do to get a win? To get a save?

Here is a situation that recently happened:

Pitcher A starts a game and goes 3 and 1/3 innings. He gets 10 outs. When he leaves the game
his team is ahead 10 to 5 and two runners are on base. His replacement, pitcher B, finishes the game and gets 11 outs. Pitcher A and B's team wins the game 12 to 9. Who is the winning pitcher and is there a save?

Here's my take on this. Pitcher B would get the win. A similar situation came up with Orem. Nate Adamson started and pitched three innings. I believe it was Marc Morgan, who pitched the fourth and fifth in a five-inning game. Who gets the win?
I talked to an official score keeper, who has worked minor league games, and he told me in a high school situation (seven innings) a starting pitcher has to pitch four innings to get the win.
Zuke