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Henry has a job for you to rob Gas Stamps from a government agency. You can gain a lot of information regarding the layout by meeting with one of the workers, Marie. Follow the waypoint to reach her apartment.
Find a suitable car and drive Marie to the hospital to visit her sister. Along the way she'll tell you all of the building's weaknesses. Some things include the back window being unlocked and a lacks amount of guards.
Gas Stamps
Once you're on your own, head to the government building. Hop the fence and head towards the bath room window.
Make sure to stay in sneaking mode to avoid being detected by the guards. You'll want to sneak up to the top level by taking the stairs on the right. Your stealth kill can kill the enemies with one easy neck break. When the two up top are finished, move to the bottom.
Kill the last guard and steal his Playboy. Instead of heading to the safe right away, take the descending stairs on the other side of the hall to enter the basement. There are more collectables here, but the true goal is the power system. Here, you can disconnect the security alarm, leaving the facility easy to rob.
Enter the director's office and nab the safe keys from his desk. Now, head to the safe just a few steps down the hall. Lock pick the barred door, and then open the safe with your keys. Since the alarm is off, you can swipe the gas stamps with little trouble. Exit the building and return to Henry.
Unfortunately, the stamps will expire tomorrow, so you need to sell them right away. Get into a fast car and drive to six different gas stations to sell off your stamps. There are five around the island your on now, so sell to those first. With time left, head across one of the other bridges to reach another section of Empire Bay to load off the last stamp. Finally, head back to Joe's to finish the chapter.
Source:
http://www.gamespot.com/features/6274410/p-4.html