Answer:
$23.40
Step-by-step explanation:
Put numbers in order: 4,5,6,6,7,8,9,9,10,10,12,12,14,15
Cut the list into two equal parts: 4,5,6,6,7,8,9 and 9,10,10,12,12,14,15
Find middle numbers: 4,5,6,6,7,8,9 and 9,10,10,12,12,14,15
Lower quartile: 6
Upper quartile: 12
The difference of the values of the first and third quartiles of the data set is 12 - 6 = 6
The area of a circle in terms of the circle's radius

is

Differentiating both sides with respect to

, you get