c2c operates a train from Barking to Dartford every 30 minutes. Tickets cost $6 - $9 and the journey takes 13 min. Alternatively, Stagecoach London operates a bus from Barking to Dartford every 5 minutes. Tickets cost $5 and the journey takes 48 min.
From Barking train to Purfleet. 13 min £5. From Plumstead High Street Plumsted Stn line 96 bus to Dartford, Pizza Hut (Prospect Place Retail Park). 48 min £3. From Thamesmead Town Centre line 229 bus to Erith Town Centre Cross Street then line 428 bus to Dartford, Pizza Hut (Prospect Place Retail Park). 57 min £4. From Barking taxi to Dartford. 21 min £70. From Barking drive to Dartford. 21 min £3. From Barking walk to Dartford. 3 h 55 min.