What are the 4 eons?

Hadean, Archeozoic, Proterozoic, Phanerozoic

just multiply 4 times 5=20

A 4-4-4-4 steam locomotive, in the Whyte notation for describing locomotive wheel arrangements, has a four-wheel leading truck, two sets of four driving wheels, and a four-wheel trailing truck

No sign of operation was mentioned. In other words, 4 4 4 4 4 4 here equals 444,444 and that should be that. If there is a common sign of operation, like "x" for "times" then it's 4 x 4 x 4 x 4 x...

22