LTNO4
Using G-R-E-S-A method.


1 G-Fn(heavy crate)=7 units
R-Fg(heavy crate)=7 units
E-Fnet?
S-Fnet= 7units+7units
A=14/unbalanced

2 G-Fn(opposite directions)=20units
R-Fg(force respectively)=10units
E-Fnet?
S-Fnet=20units+(-10units)=10
A-=10N/unbalanced

3 G-Fn(opposite directions)=20 units
R-Fg(same directions)=20units
E-Fnet?
S-Fnet=20units+(-20units)=0
A-=0/balanced