Answer
A network round trip inside one data center takes about 0.5 ms, while a round trip from California to Europe takes about 150 ms.
Also accepted: half a millisecond, 500 µs, 500 microseconds for 0.5 ms; 150 milliseconds for 150 ms.
Why
Both are approximate, but the ratio (hundreds of times) is the point: a design that makes several sequential cross-continent calls per request cannot be fast, whatever the servers do. That is why data and caches are placed close to users.