Answer:
A) Divide 20 by 2 and then add 8 to the result
Step-by-step explanation:

6*28= 168
You put 168 in the green box
As per the isosceles triangle theorem, if the two base angles are congruent then the legs are also congruent, so we must set the two legs equal to each other:
2z - 15 = 9
Add 15 to both sides:
15 - 15 = 0
15 + 9 = 24
Divide 2 from each side:
2z = 24
2z/2 = z
24/2 = 12
z = 12
Hence, the answer would be D: z = 12
Okay try to round the whole number and see if you can solve that should help you