Need help with this question not really good with math

Find the missing number. a. 3 : 24 = : 72 b. : 18 = 5 : 9 c. 6: = 36 : 36

Which of the following situations represents a linear relationship? a. theresa increases the distance she runs by 0.1 miles every week. b. the volume of a box depends on the length of box. c. the amount of money in a bank account increases by 1 percent each year. d. the population of a town doubles every 5 years.

How many $20 bills do you need to have to make $280