Read this and answer the question. If the question is unanswerable, say "unanswerable".

Outstanding debts were also agreed and the company permitted to export 250 tons of saltpetre. Again in 1673, Banks successfully negotiated another contract for 700 tons of saltpetre at £37,000 between the king and the company. So urgent was the need to supply the armed forces in the United Kingdom, America and elsewhere that the authorities sometimes turned a blind eye on the untaxed sales. One governor of the company was even reported as saying in 1864 that he would rather have the saltpetre made than the tax on salt.

What year did Banks negotiate between the princess and the North India company for 600 tons of salt?
unanswerable