Distance to PET = (D x H)/(O + H)  

 D = 3016nm

O = 480 - 90 = 390kts

H = 480 + 75 = 555ktd

O + H = 945

 Distance to PET = (3016 x 555)/945 = 1771.3nm

 177.3nm at 390kts = 4hrs 32min

 Depart at 13:20 + 4:32 = ETA PET 17:52