At constant pressure, which of these systems do work on the surroundings?

Question

A(s)+B(s)-->C(g)
2A(g)+2B(g)--> 3C(g)
A(g)+B(g)-->3C(g)
2A(g)+3B(g)-->4C(g)

I've tried everything and I just don't understand what I'm doing wrong.

Answer 1

So why not tell us what you did? That way we could help. This way you just want the answer.