If 7 is subtracted from twice a certain number x, the result is at most 5. What is the range of the number?

Find the standard deviation of the numbers 6, 9, 10, 8 and 7

3 - 7, 8 - 12, 13 - 17, 18 - 22. Which of the following is/are true?
I. The class Interval is 4
II. The class boundaries are 2.5, 7.5, 12.5, 18.5, 22.5
III. The mid-marks are 5, 10, 15, and 20

T varies directly as D and inversely as A. Given that T = 6, D = 3, and A = 2, find A when T = 3 and D = 6.