The Differential Scattering Cross Section for Particles to Scatter by 60

Multiple Choice

The differential scattering cross section for particles to scatter by 60 ^$\circ$ off a 1 mm² area target is 1.5 * 10^-18 m²/sr.A detector with an area of 2.0 cm² is placed 1.0 m away from the target in order to detect particles that have been scattered at 60 ^$\circ$ .If 2 * 10¹⁸ particles hit the target every second,how many will strike the detector every second?

A) 100
B) 300
C) 600
D) 1000
E) 2000