How long does the prime minister which has Sarla Grewal as the principal secretary serves?
Sarla Grewal:  She was the principal secretary for Rajiv Gandhi. Rajiv Gandhi: Rajiv Ratna Gandhi ( ; 20 August 1944 – 21 May 1991) was the 6th Prime Minister of India, serving from 1984 to 1989.
1984 to 1989