Answer: It is D
Step-by-step explanation:
B. it’s the change in y over the change in x
Keywords:
<em>System of equations, variables, hardcover version, paperback version, books
</em>
For this case we must construct a system of two equations with two variables. Let "h" be the number of hardcover version books, and let "p" be the number of paperback version books. If the hardcover version of a book weighs 7 ounces and the paperback version weighs 5 ounces, to reach a total of 249 ounces we have:
(1)
On the other hand, if there are Forty-five copies of the book then:
(2)
If from (2) we clear the number of books paperback version we have:

As each paperback version book weighs 5 ounces, to obtain the total weight of the paperback version books, represented by "x" in the table shown, we multiply
So, 
Answer:

Option D
Answer:
$42.88
Step-by-step explanation:
Let's create a proportion using the following setup:
cost/pounds=cost/pounds
We know that it costs $20.42 for a 10 pound turkey.
$20.42/10 pounds= cost/pounds
We don't know how much a 21 pound turkey costs, so we can say that it costs $x for a 21 pound turkey.
$20.42/ 10 pounds= $x/ 21 pounds
20.42/10=x/21
We want to find x, by getting x by itself.
x is being divided by 21. The inverse of division is multiplication. Multiply both sides by 21.
21*(20.42/10)=(x/21)*21
21* 20.42/10=x
21*2.042=x
42.882=x
Round to the nearest cent, or hundredth.
42.88=x
x= $42.88
A 21 pound turkey costs $42.88