CEDAR RAPIDS — Police arrested an 18-year-old man Tuesday after he allegedly robbed a 17-year-old who was selling a belt at Kennedy High School in northeast Cedar Rapids.Cedar Rapids police said Cortez Jacobi Riggins Jr., of Ely, met the 17-year-old boy just after 10:30 p.m. Tuesday in the parking lot at Kennedy High School on Wenig Road NE.