Answer:
8
Step-by-step explanation:
The sum of two interior angles in a triangle is equal to an exterior angle
7x - 4 + 9x + 4 = 128° add like terms
16x = 128 divide both sides by 16
x = 8
Associative Property of Addition
Your answer is 87.487699
(a) -2-(-9)=-2+9
=7
(b) -2-9=-11
(c) -2-(-9)-(-2)=-2+9+2
=9
