Blinds: $0.10/$0.25 (5 Players)
BB: $29.66
UTG: $25.58
MP: $21.58
CO: $26.85
BN: $25.00 (Hero)
SB: $25.00

no read to sb .all fold to hero, hero with A3s raise to 3bb,sb 3b to 12bb,BB fold,hero 4b all in 100bb.
1.is this a plus ev play?
2.why not 4b to 25bb or just call 3b?
3.is A3x a 100% all in?
4.what is the 4b all in range?
someone told me 4b all in here is a corrent move.I just dont understand.pls tell me why.thx.
my English is poor .sorry for my express .