Distance=speed*time
speed of light in miles=3.6 km/hr
7800 light years=7800(9.4607×10^12) km
thus the distance in miles will be as follows:
1 mile=1.60934
thus the distance from each to black hole is:
[7800(9.4607×10^12)]/1.60934
=4.5853244×10^16 miles