Mean velocity

A cyclist cycles 48 km in 2 hours 34 minutes, then turns round and goes back home in 2 hours 46 minutes. What is his overall mean velocity ?

On San Francisco bridge, a cyclist travelling at 18 km/h and a biker travelling at 36.7 km/h set off from opposite ends of the bridge at the same time. They meet after 3 minutes. How long is the bridge in metres ?

to the nearest whole number

On the 7th of November 1998, on its return from its second space journey, the shuttle Discovery had travelled 5.8 million kilometres. The mission lasted for 8 days and 22 hours. Work out the craft's mean velocity in km/h.Give your answer in scientific notation to three significant figures, note that there is one non-zero number before the decimal point, and two numbers after the decimal point.

x 10   km/h