When you write options, you get the proceed on the next day. So you will get Rs 3000 credited, but since you are writing options a margin will be blocked (approximately 40k) in your account.
1. Options expire at 0, you get to keep Rs 3000 and margin gets unblocked on expiry.
2. same as above
3. Option expire at Rs 50, so you hae to give back Rs 50 x 75 = Rs 3750. Your net loss will be Rs 750.