Which constitutional amendment provides that if the president dies resigns or is removed from office the vice president becomes the new president?

This was established generally in Article 2, section 1 of the US Constitution. But it was further clarified by the 25th Amendment (1967), which establishes that the Vice President becomes the President in this circumstance, not merely the Acting President as was previously interpreted by some.

The Presidential Succession Acts of 1792 and 1947 also provided for the death or removal of the President or his successors.