Answer:
a. 
b. 
Step-by-step explanation:
First, we need tot find a general expression for the amount of caffeine remaining in the body after certain time. As the problem states that every hour x percent of caffeine leaves the body, we must substract that percentage from the initial quantity of caffeine, by each hour passing. That expression would be:

Then, to find the amount of caffeine metabolized per hour, we need to differentiate the previous equation. Following the differentiation rules we get:

The rate is negative as it represents the amount of caffeine leaving the body at certain time.
Answer:
56 total units
Step-by-step explanation:
Here is what the plane would look like if the figure and points were drawn.
Total number of chips = 4+ 6 = 10
Number of white chips = 4
Probability of picking a white chip =

This white chip is not replaced back into the bag. This will reduce the number of white chips in the bag by 1 and reduce the total number of chips in the bag by 1.
So, now the total number of chips in the bag = 3 + 6 = 9
Number of white chips in the bag = 3
Probability of picking a white chip =

Thus, the probability of picking two white chips will be =
Therefore, option B gives the correct answer.
Answer:
The height of wall is 3 feet and length of wall is 5 feet
Step-by-step explanation:
Given as :
The Area of retaining wall = 15 square feet
Let The width of wall = W feet
The Height of wall = ( W - 2 ) feet
Now, Area of Rectangle = Height width
Or , 15 ft² = ( W - 2 ) ft × W ft
Or, 15 = W² - 2 W
Or, W² - 2 W - 15 = 0
Or, W² - 5 W + 3 W - 15 = 0
Or, W ( W - 5 ) + 3 ( W - 5 ) = 0
So , ( W - 5 ) ( W + 3 ) = 0
So, W = 5 , - 3
∴ The width of wall = W = 5 feet
And The Height of wall = ( W - 2 ) = 5 - 2 = 3 feet
Hence The height of wall is 3 feet and length of wall is 5 feet. Answer