Video Problem #1, Lecture #11: In an attempt to conquer the Earth, a group of entertainment executives rents a battalion of 7 ships to fly past the earth at a speed v = 0.9c relative to the Earth. The third ship (the Sleepy) drops a hypnotic gas into the Earth's atmosphere as it passes by. The seventh ship (the Dopey) passes by 2.5 s later (according to observers on Earth), dropping billions of mind-altering cartoon videos onto the planet's surface. Calculate the time between the passing of the Sleepy and Dopey, according to observers in the ships.