How much time will elapse in seconds before you see explosion 5400 feet away? assume speed of light is 343 m/s

The speed of light is NOT 343 m/s.  That's the speed of sound.
You HEAR the explosion after

       (5,400 ft) x (1 meter / 3.28 ft) x (1 sec / 343 meters) =  4.80 seconds.

The speed of light is 299,792,458 m/s.
You SEE the explosion after

       (5,400 ft) x (1 meter / 3.28 ft) x (1 sec / 299,792,458 meters) =

                                                                                     0.0000055 second .

Because the sun is the biggest and if the sun orbits the earth we will be dead probably

Year  1936,  lehman predicted that the earths 'inner core' is solid. she observed that the seismic signals during her study were bent and did not pass through instead bouncing back. later it was confirmed that the earth's inner core was solid made up of nickel-iron and had a molten outer core.