For the first one it would be C.
Answer:
Can't really see the question a little blur
If you notice the picture below, the amount of fencing, or perimeter, that will be used will be 3w + 2l
now

solve for "w", to see what critical points you get, and then run a first-derivative test on them, for the minimum
notice the

so. you can pretty much skip that one, though is a valid critical point, the width can't clearly be 0
so.. check the critical points on the other
Think of numbers that when they are divided by 10, the remainder is 9.
So numbers like: 19, 29, 39, 49, 59, 69, 79, 89, and 99.
Now numbers that when they are divided by 9, the remainder is 8.
So numbers like: 17, 26, 35, 44, 53, 62, 71, 80, 89, and 98.
Now the number that is alike from the two sets of numbers is n.
n=89
Double check your work.
Divide 89 by 10. Remainder of 9
Divide 89 by 9. Remainder of 8.
Hope this helps :)
This is a simple consequence of the Zero-sum problem: https://en.wikipedia.org/wiki/Zero-sum_problem