context: Pieter Willem Botha, (Paul-Roux, Free State, 12 January 1916 – Western Cape, 31 October 2006), usually called "P.W." and "Die Groot Krokodil" in Afrikaans which means "The Big Crocodile", was the Prime Minister of South Africa from 1978 to 1984 and also the president from 1984 to 1989.
question: When did Pieter Willem Botha serve as prime minister?
answers.text: 1978