First, you're going to need a grenade launcher. As you reach the end of the level ( shown in Thumbnail of clip above before payed) go to the hall way to the left. Stand back, and shoot the grenade launcher at the other end of the hallway (right side). Hit the cages on the far wall and the achievement should come up. if it doesn't, simply switch to your primary and there are several moneys to the left of you.