Daniel hiked 4 5 8 miles on Saturday and 4 1 2 miles on Sunday. How many miles did he hike in all? HELP PL GIVING BRAINLIEST PLZZZ HEL THANX

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?