CAN'T vs CANNOT

Are these both possible?

1 Why can't people spell my name right?

2 Why can people not spell my name right?

3 Why can't I ever/can I never remember it?

Could you also please tell me if these sound right?

1 How do I know which number to divide into/by which number.

I never know which number to call.

2 Do you know which building you want to live in?

3 Do I have to proceed differently with this contract?/Is this contract any different from the others?

4 I make in 1 day what you make in a month./ I make 100 dollars off/on ever deal.

5 It would be wrong if I asked him if he could lend me money knowing he was broke./to lend me money knowing he was broke.

Thank you