Firstly, we can find the circumference of the circle by using this formula: pi (3.14, but some questions require you to multiply by the actual pi) x diameter.
So, assuming that we are multiplying just by 3.14 and not the actual pi, the equation would look like this for question 1 :
C=3.14 x 52 = 163.28
This is how I would solve it. I hope it’s correct and that it helps!