[Cosimo]

You have a 42% chance to win this hand, so a call is justified. Specifically, there is a 42% chance that you will make your straight or flush. Note that you could make your flush but someone else can fill up and beat you, or have a higher flush. Ditto for the straight: someone could fill up. On the other hand, you could hit two running cards to get an overset. These about average out (tho not exactly), so I'd say 42% is close enough.

With a greater than 33% chance to win, you can call a pot-sized bet (assuming no further betting). If someone bets pot and someone else calls, it's an easy call. Since BB only has $4 behind, it's an easy push.

You have 15 outs (assuming your str8 draw is to the nuts, and the flush will be good). That's about 2:1 for the next card. If there's going to be further betting, you can call a pot bet even if there's no other callers.

It doesn't matter that you're behind now. Hold'em is played with 7 cards.