Answer:
The value of x is 18°.
Step-by-step explanation:
If I remember correctly, I believe the sum of opposite angles 89° and 51° are also the sum of the angles (5x - 8)° and (3x + 4)°. So, going off that..
If 89° + 51° = 140°; then (5x - 8)° + (3x + 4)° = 140.
(5x - 8)° + (3x + 4)° = 140
8x - 4 = 140° Combine like terms
+ 4 + 4 Add 4 to both sides
8x = 144
8 8 Divide both sides by 8
x = 18°
Hope this helps,
~ Nicki ~
