I needdd help plsss

In a graph with several intervals o data how does a constant interval appear? what type of scenario produces a constant interval?

Which property was used to simplify the expression? 3c+9 +4c=3c+4c+9

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?