They are abstract "word" problems, offered for the purpose of giving the
student of high school mathematics valuable practice in the application
and manipulation of the concept of "percent".
Often, some time spent in solving practice-examples such as these can
lead to the phenomenon known as "learning", whereby the student comes
to know, understand, and possess competence in a topic where he or she
was previously ignorant and incompetent.
It is important to realize that the practice is the vital component in the process,
whereas the answers alone have no value at all.
First, find the mean. You'll need it to compute the variance.

The variance of the sample is then computed with the formula

The standard deviation is the square root of the variance, so

Pick any value for x, like x = 0, plug it into the equation, and get the value for y. For x = 0,
2(0) + y = 5
y = 5
The ordered pair is (0,5). Find other ordered pairs using the same reasoning.
One can solve this by first using order of operations, and then combining like terms.
First is parenthesis
9x + 2x(9) - 2(9x)
Now we do the multiplication
9x + 18x - 18x
Now we combine like terms
9x