The opening monologue in this episode was narrated by John Deegan. But for the last line, he says it after transforming into Superman.
Dr. John Deegan:
My name is John Deegan, and I'm from Gotham, a city in grave need of heroes. As a doctor at Arkham Asylum, I did my part by protecting this city from the criminially insane. The world didn't understand my methods, so I worked in secret until, one ...
In order for Supergirl and Flash to cover the circumference of the Earth (24,901 miles/40074274.9 meters) as fast as they did, they would need to travel at a speed of 40074274.9 meters per second or 89,643,599.90157 miles per hour, which is much faster than Mach 7 (2,382.03 meters per second).