Hi I have a question about this math. So, I have the answers, i'm just having trouble on how to get to the answers.

1. This is the problem ,A rancher wishes to enclose a rectangular are into two separate regions one for cattle and the other for sheep. There are 240 yards of fencing available. What are the dimensions that will enclose the largest area? And the answer is 40 by 60 yards. I'm not sure what I got wrong because I got 60 by 60 yards.

2. What is the derivative of xy+y²=2, the answer is dy/dx= y/x+2y

3. Find the equation of the tangent line, X³y+y³-3=6xy @(2,-1), the answer is y=-6x+11

4. Determine possible Maximum & minimum points and increasing & decreasing intervals, 2x²+3x²-36x+5, the answer is Max(-3,86) Min(2,-39), inc (-infinity, -3)U(2, infinity), dec (-3,2)

5. Determine possible Maximum & minimum points and increasing & decreasing intervals

3x⁴-4x³-36x²-5 , the answers are max(0,-5), min (-2,-69) and (3,-194), inc(-2,0)U(3, infinity), dec (-infinity,-2)U(0,3)

6. Determine possible Maximum & minimum points and increasing & decreasing intervals, x³-3x²-24x+2, max(-2,30), min (4,-78), inc(-infinity, -2)U(4,infinity), dec (-2,4)

7. Determine Possible Inflection Points & Intervals of Concavity x+4/x-4, the answer says no IP, concave up(4, infinity), and concave down(-infinity, 4)

I have tried to solve these but I got the wrong answers, so if you could please give me show me how y'all got the answer. I'm not sure what I did wrong, but I will compare and contrast what I did wrong.