Until 1998, Shearer was paid $30,000 per episode. During a pay dispute in 1998, Fox threatened to replace the six main voice actors with new actors, going as far as preparing for casting of new voices. The dispute, however, was resolved and Shearer received $125,000 per episode until 2004, when the voice actors demanded that they be paid $360,000 an episode. The dispute was resolved a month later, and Shearers pay rose to $250,000 per episode. After salary re-negotiations in 2008, the voice actors received $400,000 per episode. Three years later, with Fox threatening to cancel the series unless production costs were cut, Shearer and the other cast members accepted a 30 percent pay cut, down to just over $300,000 per episode. On May 13, 2015, Shearer announced he was leaving the show. After the other voice actors signed a contract for the same pay, Shearer refused, stating it was not enough. Al Jean made a statement from the producers saying "the show must go on," but did not elaborate on what might happen to the characters Shearer voiced. On July 7, 2015, Shearer agreed to continue with the show, on the same terms as the other voice actors.
Question: How many years passed between Shearer's lowest salary and his highest salary?
Answer: 10