[SG] newbie SG question on line of sight/line of fire

I _know_ I'm missing this somewhere, but do all figures of a unit have
to be 
able to see the target to shoot?  Example: 3 figures of a 7 figure squad
are 
in woods and can't see the target - do I multiply the small arms
firepower by 
7 or by 4?  And do all 7 figures have chance of being hit by enemy fire
or 
only the 4 in the open?  Thanks,
Jed Docherty