i am not too sure if i am correct in this but i will give it a go. i apologise if i am incorrect. In finding the diameter the equation C/π. in finding the radius the equation is (C/π)/2
Part 1
Q2) c=650πcm
650 X π= c so d must be 650cm
Q4) c=241πcm
241 X π= c so d must be 241
Q6) c=802cm
c/π=d =802/π= 255.28cm (2DP)
Q8) c=962cm
c/π=d = 962/π= 306.21cm (2DP)