One answer would be15669012
The error bars are used to indicate the variability of the data presented in a graph.
There are several quantities that can be used to generate error bars in the graph. These are:
standard deviation
standard error
confidence interval
Usually, one standard deviation above and below the mean is used although it is advised to indicate which variability data is used to generate the error bars in the graph since the 3 quantity given are not equal.
Answer:

Step-by-step explanation:
In the equation: 
x's can be simplified and y's can be simplified!
Always remember that for exponents, you subtract the powers when dividing
so for x: 15-8 = 7
for y: 9-3 = 6
so the final answer is: 
18 / 2 = 9 || 9 x 3 = 27. Therefore, 27 students are registered in Bob’s class.
Jenny's algebraic expression:
y = 33d
where y is the total number of posts
total tweets in 5 days
y = (33)(5)
y = 165 tweets
Antonio's expression:
y = 5d
total tweets in 5 days
y = (5)(5)
y = 25 tweets
Altogether they have posted:
165 + 25 tweets = 190 tweets in five days