I told you the ratio in-game the other day in MeowLady's shop. It's normally 7 PD's = 1 DT from what I've seen in chatbox and in posts. This would probably cost you 3 DT's (21 PD's) or you could run Int. Defense System [IDS] (Episode 1 Quest) and get minimum 2 PD's per run on VH then pay 2 DT's (14 PD's) and pay 6 PD's to cover the rest. You got 4 PD's now so 1 run of Int. Defense System should get you what you need. There's a hidden box that floats high up to the far right of the room with everything floating that has a chance at giving you a PD. The other 2 are at the end of the quest after the waves of enemies in Seabed in boxes before you exit through portal. I'm not sure if there's any other PD's that drop from that quest but good luck. If I'm online in-game I'll help you. I Need to run errands today though so won't be on until later.