Can please someone help me? The question is in the picture. Thank you

How to use order of operation in 20 divide by 4 multiply 5 = 1

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?

Lowest fraction using common term 28/35