A former Stockbridge High School teacher accused of threatening to kill the principal signed a severance agreement that will cost Stockbridge Community Schools about $135,000. Lynnette Brown, who resigned last month, will receive a lump sum payment of $50,000, reduced by necessary withholdings, on or before June 30, according to the agreement, obtained this week through a Freedom of Information Act request. This is in addition to about seven months of pay and benefits, totaling about $52,402; insurance benefits, which cost $25,645, this school year, through August 2012; and some other provisions.