The area of circle b is 36 times greater than the area of circle
a. if the radius of circle b is 12 feet, what is the radius of circle a?

The formula for area of a circle is pi r^2.
Circle A= pi a^2
Circle B= pi b^2

Now if the area of circle B is 36 times greater than the area of circle A, we can translate than into:
areaB=36*areaA
pi b^2 = 36 pi a^2
pi b^2 = 36 pi 12^2 (sub in variables)
b^2 = 36*12^2 (divide pi from both sides)
b^2 = 36 * 144 (solve 12^2)
b^2 = 5184 (simplify right hand side)
b = 72 (take square root on both sides)
Your answer is 72. 

Have a nice day :D

Answer: d. 39 cmin the diagram, the approximate length of the minor arc de is 39 centimetres.step-by-step explanation: the formula for the length of an arc in a circle is as displayed below.let the length of the minor arc de = xx = 2( pi )r × angle of sector / 360°from this, we will substitute the values given from the problem into the formula to obtain the length of the minor arc de.x = 2( pi )r × angle of sector / 360°r = radius = 25cmpi as an approximate value = 3.14angle of sector = 120°x = 2( 3.14 )( 25 ) × 120° / 360°x = 157 × 1 / 4x = 39.25x = 39 ( rounded to the nearest whole number as an approximate value )