An ion in a mass spectrometer follows a semicircular path of radius 14.8. What is the distance it travels?
The circumference of a circle is (2π · the circle's radius).
The length of a semi-circle is (1π · the circle's radius) =
(π · 14.8) = 46.5 (rounded)
(The unit is the same as whatever the unit of the 14.8 is.)