Mr. Smith started the school year with 26 students in his class. If x students moved out of his class, which expression represents the number of students left in the class? The answers:
x + 26
x - 26
26 - x
26 + x
Please help me quickly before 11

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?