Answer:

Step-by-step explanation:
The difference of two cubes formula is given as:

Number 21 is the first answer a.) 8



now, with that template above in mind, let's see this one

A=3, B=1, shrunk by AB or 3 units, about 1/3
C=2, horizontal shift by C/B or 2/1 or just 2, to the left
D=4, vertical shift upwards of 4 units
check the picture below
The total length of the circle is calculated by the following formula:
Lenght = 2.π.r
As r = 4c
Then,
Lenght = 2.π.4
Lenght = 8π centimetrs
Now use the rule of 3
But we have to know:
...<..> ...
Then,
8π ________ 2π <= 360°
x ________ 3π
2π . x = 8π . 3π
x = (8π . 3π) / 2π
x = (8 . 3π)/ 2
x = 12π centimenters
x ~ 37,69 c