The radius of a circle is 20 cm. Find its circumference in terms of Pi

Can someone pls ! pls answer all. no explanation needed..

Typically a point in a three dimensional cartesian coordinate system is represented by which of the following answers in the picture !

Will mark ! (10 points also! ) if x varies inversely with y and x =6 when y= 10, find y when x=8 a. y=4.8 b. y=7.5 c. y=40/3 d. y=4/15