A decimal point. Im guessing you meant to say tenths instead of tens
Having the angle in radians and the diameter of the circle we can easily calculate the length using the following expression
Length = angle(radians)*diameter/2
With this expression we can easily deduce the perimeter of a circle (length of the full arc)
Length = Perimeter = 2*pi*r
There is only one operation involved in this process
Line point L would be the midpoint of question 3.