9 + ( -10 ) + 11 + ( - 12) + 13 + ( - 14 ) + 15 + ( -16)
= -1 + 11 + ( -12 ) + 13 + ( -14 ) + 15 + ( -16 )
= 10 + ( -12 ) + 13 + ( -14 ) + 15 + ( -16 )
= -2 + 13 + ( -14 ) + 15 + ( -16 )
= 11 + ( -14 ) + 15 + ( -16 )
= -3 + 15 + (-16 )
= 12 + ( -16 )
= -4