As the Seattle Sounders prepare for the second leg of their Western Conference Semifinals series with FC Dallas on Sunday (6 p.m. PT; FS1/KIRO 97.3 FM/El Rey 1360AM) here is a breakdown of the aggregate rules and how the Sounders can advance.

The conference semifinals and conference finals in the Audi 2016 MLS Cup Playoffs are home-and-home two-leg series based on aggregate scoring.

So what does that mean?

Each team plays at home once, and whichever team has more combined goals at the end of the two-game series advances. If the score is tied after the two matches, the first tiebreaker is away goals. If the teams have the same amount of away goals, then they will play extra time in the second leg and will go to penalty kicks if the score is still tied.

So what does that mean for the Sounders?

Seattle defeated FC Dallas 3-0 at home in the first leg of the Western Conference Semifinals on Sunday. Dallas will need to win 3-0 in Frisco, Texas, next Sunday to force extra time or at least 4-0 to advance. But if the Sounders score, FCD will need at least five goals because the Sounders would hold the away goals tiebreaker.

Here’s what that looks like in graph form, via Steve Fenn on Twitter.

ESPN’s Soccer Power Index projects the Sounders have a 94 percent chance of advancing to the Western Conference Championship.