Forgetting the number of rakaats in salaah

Q: During a four rakat prayer, if one has forgotten whether they are in rakat two or three, and they decide two is more likely so they sit and read attahiyyat, do they also have to read tahiyyat after the next rakat, which they assume is the third one?

If one is not sure whether they are in rakat one or two, and they decide two is more likely so they sit and read attahiyyat, do they also have to read attahiyyat after the next rakat?

Editing one's pay slip to get a better salary

Q: I am working in a company in night shifts and I am planning to switch to another company due to salary concerns. To get a higher salary I have edited the payslip of my company's current salary because most of our collegues and I feel that the companies are exploiting us by paying us a less salary and they are getting higher profits. I feel like it is cheating because I am editing my current salary from 17000 and faking it to 21000. I have already been selected and if I join that company, is my income Halal or Haram?

Getting a fixed retainer on one's teeth

Q: Do you think I can get a fixed (permanent) retainer as opposed to a plastic retainer for my teeth which I can get off and on, just for the simple reason that I feel like a plastic retainer which you take on and off and have to possibly wear forever, will be a nuisance? There have been cases where not wearing your retainer will result in your teeth shifting, which would be a huge waste of money that was spent on braces. I feel like a fixed retainer will be easier for me.

How should a Musaafir calculate if he has to perform full salaah or qasr salaah?

Q: How can I calculate 15 days during a journey in order to know whether I need to perform qasar Salaah or full salaah. Suppose I reach a destination on 1st Dec 05:30 pm and plan to stay till 15th Dec 05:30 am.

Do I need to to take into account till 15th Dec 5:30 pm (360 hrs) as it is less than 360 I should offer Qasr even though it is 15th day ?