Step-by-step explanation:
we know that sum of all angles of a triangle is 180°
so, angle N + angle O + angle M = 180°
=> (-5b+16)+(-b+8)+(-9b-9) = 180°
=> -5b+16-b+8-9b-9 = 180°
=> -15b+15 = 180°
=> -15b = 180-15
=> -15b = 165
=> b = -165/15
=> b = -11
angle N => -5(-11)+16
=> 55+16 => 71
angle O => -(-11)+8
=> 11+8 => 19
angle M => -9(-11)-9
=> 99-9
=> 90
