In German, the formation of tens is accomplished by adding the suffix "-zehn" to the corresponding number. This suffix has a peculiar meaning, since it literally translates as "ten". However, in the context of numbers from 20 to 90, it is used to form numbers representing tens.
Thus, to form numbers from 20 to 90, a prime number (2, 3, 4, and so on) is taken and the suffix "-zehn" is added. This rule applies to tens, and this is how the numbers representing tens in German are formed.