Is permissible to buy/sell with non-Muslim?
Yes buying/selling for a Muslim with non-Muslim is permissible as regards what is lawful.
I took a housing loan from the bank for a 20-year period. Four years have passed, and I recently learned that this loan is usurious. I wish to perform Umrah. Am I permitted to perform it? If not, what should I do?
You are permitted to perform Umrah. Strive to repay the debt in hopes of reducing the amount of usurious interest. Allah Says (What means): "And there are others who have acknowledged their sins. They had mixed a righteous deed with another that was bad. Perhaps Allah will turn to them in forgiveness. Indeed, Allah is Forgiving and Merciful." [At-Tawbah/102]. And Allah Knows Best.
What is the ruling on smoking?
All Perfect Praise is due to Allah, The Lord of The Worlds
Smoking is forbidden (Haram) since it is harmful to one`s health as confirmed by trustful physicians, and Islam has forbidden taking anything that causes harm. The Prophet (PBUH) said: "There should be neither harm nor reciprocated harm." [Ibn Majah and Ahmad]. And Allah Knows Best.
I work at a company that provides cash advances of 800 dinars, 1000 dinars, or 1200 dinars, depending on the employee’s years of service. An administrative fee of 40 dinars is deducted from the amount in the first month, and the remaining amount is repaid in installments. What is the ruling on this, knowing that the deducted amount (40 dinars) is fixed?
We fear that the deducted amount may be a means of circumventing interest (Riba). If the deducted amount is equal to or less than the actual administrative expenses, then there is no issue, as some scholars permit the borrower to bear the costs of documenting and managing the loan. However, piety suggests refraining from taking this loan under these conditions, as dealing with private individuals and companies is not the same as dealing with the state, which spends from the public treasury. And Allah Knows Best.