Hello,

So d is such that

Euler's theorem :

Here, n=101 and is prime.

3d has to be congruent to , i.e.

--------

Why ?

--------

So we want to find the inverse of 3 modulo 100.

But you have to be careful, because either I've confused myself, either this is a particular case. In general, the number which would be at the same place as 101 is rarely prime.