Step-by-step explanation:
I assume we are simplifying
1) -6k+7k = k
2) 12r-8-12 = 12r-20
3) n-10+9n-3 = 10n-13
4) -4x-10x = -14x
okay so
117° + angle a = 180° (supplementary angle)
angle a = 180 - 117
= 63°
then angle a + angle b + 81° = 180° ( angle sum property)
so... 63° + angle b + 81° = 180
144 + angle b = 180°
angle b = 180 - 144
= 36°
hope this helps.
Lattice method, or Calculator.