I think you meant for the three plays. If I'm incorrect, leave a comment below this answer and I'll edit my answer.
Play One = + 7 yards. Play Two = - 15 yards. Play Three = -18 yards
Net = 7 - 15 - 18 = - 26 yards. That means that they are 26 yards behind where the ball started for the first play. They are not in a very good position.