Answer:
a. 46.5 mph
b. 32.3 kph
Explanation:
If the speed limit is 100 km/hour we and this equals 62 mile per hour we can determine how many kilometers is in miles and vice versa:
WE can do this as:

Therefore the 0.62 miles per kilometer
a) For 75 kph we can use the conversion we determine to convert to miles per hour:

It takes a speed limit of 46.5 mph for a 75 kph limit
b) For 20 mph we can use the conversion we determine to convert to kilometers per hour:

It takes a speed limit of 32.3 kph for a 20 mph limit