What's the amperage on a circuit breaker that's "linked" together?
Each circuit is rated 20 amperes.

Handles are typically tied together when all the breakers are supplying a single piece of equipment. For example, in a 120/240 volt single phase system, two breakers might be tied together for a piece of equipment that requires 240 volts. Three breakers tied together would be common for a 3 phase systems.

In all situations, the circuits are still rated whatever is listed on the handle, not the total of the breakers.