Simplify the following text for a Grade 9 native English-speaking person.
Original: Sir Joseph Cook , GCMG ( 7 December 1860 â `` 30 July 1947 ) was an Australian politician and the sixth Prime Minister of Australia .
Simplified: Sir Joseph Cook ( 7 December 1860 â `` 30 July 1947 ) was the sixth Prime Minister of Australia from June 1913 until September 1914 .