Two farmers agree that pigs are worth $300 and that goats are worth $210. When one farmer owes the other money, he pays the debt in pigs or goats, with ``change'' received in the form of goats or pigs as necessary. (For example, a $390 debt could be paid with two pigs, with one goat received in change.) What is the amount of the smallest positive debt that can be resolved in this way?
<spanclass=′latex−bold′>(A)</span>$5<spanclass=′latex−bold′>(B)</span>$10<spanclass=′latex−bold′>(C)</span>$30<spanclass=′latex−bold′>(D)</span>$90<spanclass=′latex−bold′>(E)</span>$210