If dynamic text box 'hp' = 0 or less, than play scene

if dynamic text box ‘hp’ = 0 or less, than play scene
how do i do that. when my badguys shoot they dont do even numebrs of dmg. so it might be -1 or -5 etc…

one more thing. if u know how to do this. i want to play a scene when all guys die. like i was thinking, to do something like this,
on clip load
person = 0

when he dies on the last frame, i put person = 1
and for my actions frame put something like this
if person = 1 and person2 = 1 and person3 = 1 then
gotoandplay scene “win”

can u help me out a bit?