Rouge Tomato can be found on the rocky cliff just in front of the entrance to the city. Go there and kill him. He's pretty strong (as for your current level) but you should have a stock of potions on you and he shouldn't cause you any trouble. After you dispose about half of his HP he jumps down the cliff. Run after him and finish him off. Look out for the wolves prowling there. Try to lure your target to a place without enemies nearby. After the fight get back to Rabanastre, go to "Sandsea" and talk with Tomaj.
Bounty: 300 gil, 2x Potion, 1x Teleportstone