a speed sign in England reads 30. km/hr,over what speed in mph (miles/hr) would you get a ticket?
You can look up conversion factors to find one that converts exactly as you want it but I find it easier to remember a few factors and forget about looking up an exact one.
There are 1000 m in 1 km.
There are 100 cm in 1 m.
There are 2.54 cm in 1 inch.
There are 12 inches in 1 foot
There are 5,280 ft in 1 mile.
Put all of that together. I get something like 18.5 mph.
Here is a site that converts just about anything to anything. http://www.onlineconversion.com/speed_all.htm
Also, you can go to google.com and type in "30 km/hr to miles/hr" without the quotation marks, hit enter and the answers pops up.