10. B
11. D
12. C
13. B
14. B
15. D
Width=w
length=(40-2w)/2=20-w
A=w(40-w)
A=40w-w²
A'=40-2w=0
2w=40
w=20
20x20 is the size of the pen having the greatest area. this tells us the largest rectangle for a given perimeter is a square
Answer:

Step-by-step explanation:
- The sum of a number n and 5 => n + 5
- Thrice the sum of a number n and 5 => 3(n + 5)
- At most means "less than or equal to", the sign of which is "≤"
<u>So, the inequality will be:</u>
3(n + 5) ≤ 100
![\rule[225]{225}{2}](https://tex.z-dn.net/?f=%5Crule%5B225%5D%7B225%7D%7B2%7D)
Hope this helped!
<h3>~AH1807</h3>