The mean distance from the Earth to the Sun is c gigametres (Gm), where c = 150 and 1 Gm = 10⁹ m. The mean distance from Pluto to the Sun is d terametres (Tm), where d= 5.91 and 1 Tm = 10¹² m. Express d as a percentage of c. Give your answer in standard form.
please help, I don't understand how to get percentage