The answer to the question above is x=-4.5
<h2>The Correct answer is B)</h2><h2>This answer is verified by brainy.Com✓</h2>
Solution: We are given:

Using the empirical rule, we have:
covers 68% of data.
Also the percentage of values below mean = Percentage of values above mean = 50%
Now, let's find the z score for x=20

Therefore, the percentage of values greater than 1 standard deviation above mean 
Expected number of students = 16% of 100 = 16
The answer is very simple:
$50 multiplied by 2 (Cause it's 200%) equals to $100
$50 multiplied by 1,2 (Cause it's 120%) equals to $60
Then, you just do the substractions, so you get $40.
Hope I helped u
Your proportion should look something like this

After cross multiplication, you should end up with this equation

After dividing 4 on both sides, you should get that x=9