valid,non valid arguments

Prove which of the following arguments are valid or non valid:

1)if London is in France then Paris is in England.But London is not in France,hence Paris is not in England.

2)if London is in England then Paris is in France.But Paris is not in France ,hence London is not in England.

3)if London is in France then Paris is in England.But London is in France, hence Paris is in England.

Surely the 1st one is true,the 2nd one false and the 3rd one also false .

But why do they ask us to prove that ,what is there to prove??