May I please receive help?

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?

What adds to be the bottom number but also multiplies to be the top number with 8 on the bottom and 15 on top

Which number produces an irrational number multiplied by 1/3