One of three teenage boys charged with burning the Sacajawea Middle School library on Sept. 8 pleaded guilty Tuesday and was sentenced to a maximum standard 75 days of detention. Harrison M. Seaborn, who turns 16 next month, also was ordered to pay $100,000 in restitution – along with his co-defendants, 16-year-old Quinten M. Glenn and 15-year-old Cody L. Baker, if they also are convicted.