Answer: the system of equations that represents this situation are
12x + 6y = 180
x = 2y
Step-by-step explanation:
Let x represent the number of hardcover books that were sold in a day.
Let y represent the number of paperback books that were sold in a day.
The discount bookstore sells hardcover books for $12 and paperback books for $6. The total sales that day were $180. It means that
12x + 6y = 180
The number of hardcover books sold that day was twice the number of paperback books. It means that
x = 2y
let's notice, this is a Cube, namely all equal sides, and mind you it has 6 sides, Check the picture below.

Answer: The number of calories increased by 20%.
Step-by-step explanation:
Given : The doctor recommended that Mike increase the number of calories he burns working out from 1,500 to 1,800.
Previous number of calories he used to burn = 1,500
Increase in calories = 1800-1500=300
Now , the percent increase in calories = 

Hence , the number of calories increased by 20%.
A. 4 (is the only factor for expression -48xyz -24xy +40)