find the smallest positive integer b which satisfies 3^56=b(mod7)

I am very new to modular arithmetic and I stubbled upon this question.

Wouldn't 'b' have a specific solution.

Asking for the smallest positive integer b confuses me.

when I put 3^56 into my calculator or into Excel i get a rounded answer. This also surprised me a little.

The calculator doesn't have enough digits, so there is no enigma there.

But why does Excel round? I think the last digit has to be 1, and excel just gives about 15 places and then a stack of zeros.

Can you set excel to give more acuracy? I guess that this is a second question.

This is it for me. would someone like to add input please.