The speed limit on a interstate highway is posted at 75 mi/h.

 Part 1

1 mile is roughly equivalent to 1.6 km's

 

So   75 x 1.6 = 120 km/h.

 

Part 2

 

 1 mile is equal to 5280 feet, one hour is 3600 seconds.

 

So 5280/3600 = 1.4667 feet/sec.