On that note, here's a walkthrough for missions 36 through 40.
Mission 36: Billy (cost: 4 charges, reward: 2700 cash)
Billy is tired of being bullied, and the guy picking on him plans to jump off the tallest diving board. What an opportunity to take him out, right? Line him up in your sights and move your scope to compensate for distance, then plant one in his head. That'll be the last dive he ever takes.
Mission 37: Mr. Haynes (cost: 5 charges, reward: 3200 cash)
Your latest client can't wait to take over a new restaurant, but the current owner stands in the way. He never goes outside, which makes him easy pickings for a bullet in the head. When you first hit the scene, you'll see a guy standing in the doorway and one sitting outside. Aim your weapon in the small windows next to the doorway. Judge for distance while aiming towards the second row of small windows, and you'll take him out nice and cleanly.
Mission 38: Mr. Grimes (cost: 5 charges, reward: 3500 cash)
Your client explains that his intended target has escaped assassination before, but he's going off on a mountain climbing excursion that'll make him easy pickings. When you first line up your target, he'll be coming down from the top, and moving rather quickly. However, he'll pause midway through his descent to make some adjustments. Line him up and take a quick shot, because otherwise, he'll slide down the rope to safety.
Mission 39: Mr. Williams (cost: 4 charges, reward: 1900 cash)
You're on a protective mission again, this time preventing your client and his buddy from being ripped off by fellow dealers. You'll want to focus on the two guys on the left. Go ahead and concentrate your first bullet on the one talking with your client. After shooting him, the other guy will start shooting and take cover behind some rocks. Wait for him to pop his head out in the open, then let him have it.
Mission 40: Donald (cost: 4 charges, reward: 1950 cash)
We're not sure why Donald wants to kill someone at the grocery store, but no matter. It's time for you to deliver. There will be two guys talking behind a store window and your target will be on the left. Focus on him, make minor adjustments with your scope and take the shot. You'll know you're successful by the blood stains that appear on the window pane.