Find area of the largest rectangle with lower base on x axis and upper vertices on the parabola y=27-x^2 Show the max and min

1. A rectangular garden 450ft^2 in area is to be fenced off against rabbits. If one side of the garden is protected by a barn wall find the minimum amount of fencing needed
2. y= x/x^2+4
3. Find the area bounded by f(x)= 16-x^2 and the x axis from x=1 to x=3 using 4 rectangles.