Answer:
C.20
Step-by-step explanation:
Confidence interval concepts:
A confidence interval has two bounds, a lower bound and an upper bound.
A confidence interval is symmetric, which means that the point estimate used is the mid point between these two bounds, that is, the mean of the two bounds.
The margin of error is the difference between the two bounds, divided by 2.
In this question:
Lower bound: 70
Upper bounf: 110
Margin of error:
Thus the correct answer is given by option C.