For this case the volume of the box is given by:
V = l * w * h
Where,
V = 24 feet ^ 3
Substituting values we have:
24 = l * w * h
Clearing the value of h we have:
h = 24 / (l * w)
Answer:
The height in terms of the other sides is:
h = 24 / (l * w)
If x represents the width of the poster (including borders), the area of the finished poster can be written as
.. a = x*(390/(x -10) +8)
.. = 8x +390 +3900/(x -10)
Then the derivative with respect to x is
.. da/dx = 8 -3900/(x -10)^2
This is zero at the minimum area, where
.. x = √(3900/8) +10 ≈ 32.08 . . . . cm
The height is then
.. 390/(x -10) +8 = 8 +2√78 ≈ 25.66 . . . . cm
The poster with the smallest area is 32.08 cm wide by 25.66 cm tall.
_____
In these "border" problems, the smallest area will have the same overall dimension ratio that the borders have. Here, the poster is 10/8 = 1.25 times as wide as it is high.
The maximum height of the projectile is the maximum point that can be gotten from the projectile equation
The projectile reaches the maximum height after 5 seconds
The function is given as:

Differentiate the function with respect to t

Set to 0

So, we have:

Collect like terms


Solve for t


Hence, the projectile reaches the maximum after 5 seconds
Read more about maximum values at:
brainly.com/question/6636648