Answer
a) $2.4\times10^{5}km/h$
b) $10min$
Work Step by Step
a) Speed in km per hour =
$(120 paces/1 min) \times (7 leagues/1 pace ) \times ( 4.8 km/1 league )\times (60 min/ 1hr)=2.4\times10^{5}km/hr$
b) The circumference of the earth is approximately 40000km. The time taken to march around the earth is found by dividing the distance by the speed.
Time of travel = $40000\times (1hr/2.4\times10^{5}km)\times (60min/1 hr) = 10min$
