Answer :
1 day = 86,400 seconds
1 mile = 1,609.344 meters
Speed = (3 x 10⁸ m/s) x (86,400 s/da) x (1 mi/1,609.344 m)
Speed = (3 x 10⁸ x 86,400 x 1 / 1,609.344) (meter-sec-mile/sec-day-meter)
Speed = 1.61 x 10¹⁰ mile/day
Speed = 16.1 gigamiles per day