What is the measure of the radius 20.1?

You mean how to measure circumference and area of a circle, so there are some formulas to measure it.Now to measure circumference of the circle the formula is 2.pi.r(remember pi is always 22/7.Here r is 20.1).So applying this formula lets find the circumference, that is 2x22/7x20.1=126.34285714285714285714285714286

Now to find area of a circle you have to apply the formula that is pi.(r)square.Lets find the area applying this formula, 22/7x(20.1)square=(1269.7457142857142857142857142857)square thats it.

More:Instead of taking pi as 22/7 you can take it as 3.14.But if you will calculate 22/7 the answers will be 3.1415926535897932384626433832795 so in short take it 3.14.

Thanks