Help me with this short math equation olz

Aboat costs 19200 and decreases in value by 12% per year. how much will it cost in 5 years

What is the value of x when x + 7 = 21?

Assume that there is a 11% rate of disk drive failure in a year. a. if all your computer data is stored on a hard disk drive with a copy stored on a second hard disk drive, what is the probability that during a year, you can avoid catastrophe with at least one working drive? b. if copies of all your computer data are stored on four independent hard disk drives, what is the probability that during a year, you can avoid catastrophe with at least one working drive?