Can anyone help?

I try to stick with a line up that includes at least 1 ranger as well. However I have come across a few points where I just have to wait to gain some more levels on my characters

I used a lineup of one ranger, one chemist, and 3 melee units. Then I hit him with can after can of nerve agent. They can't fight back if they're sleeping. I barely edged out a win! I'm no expert at this game and I'm just learning to but that's how I figured it out maybe it'll help you to

Use 1 ranger, 1 chemist and 2 infantry and use those things produced by the chemical workshop.