hello! i need help

Suppose that R is a relation on the set of positive integers such that:

aRb if and only if l(a) = l(b)

where l(x) is the number of decimal digits of x. (for example l(122) is 3)

we already proved that R is an equivalence relation..the question is:

Considers the set of numbers formed from the 4 digits 1, 2, 3 and 4.

What is the equivalence class of 12?

thank you