We will have to use the formula for the area of a trapezoid on this problem, which is (
and 
are the bases of the trapezoid and 
is the height):
All we need to do is substitute the information we are given into our formula:
Now, let's just simplify the equation:
The missing base has a length of 13 units.
Are there any answer choices because this question has multiple answers.
Answer: 1308
Step-by-step explanation:
Given : Level of confidence = 0.97
Significance level : 
Critical value : 
Margin of error : 
If prior proportion of population is unknown , then the formula to find the population proportion is given by :-
Hence, the minimum sample size needed =1308
38 because 80% of 20 is 18 and then add the 2
