We are given the speed of the shuttle as:
speed = 28,000 miles / hour
We know that:
1 mile = 5280 ft
24 hour = 1 day
Therefore by conversion:
speed = (28,000 miles / hr) * (5280 ft / 1 mile) * (24 hr / day)
speed = 3,548,160,000 ft / day
In 2 significant figures:
speed = 3.5 x 10^9 ft / day