Hi, I have a few problems which i can't solve

1) need to prove (m+dk)mod d = m mod d (where m, d and k are integers and d does not equal to zero)

2) if r is any rational number and s is any irrational, then r/s is irrational

3) prove that there is at most one real number b with the property that br = r for all real numbers r.

Thank you