PLEASE HELP ME WITH THIS HOME WORK if i keep a low grade i could fail this class i just NEED to pass this i have to watch my siblings in and after class and maintain good grades just someone PLEASE HELP ME

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?