need help please

3. Find the value for x so the box shown below has the largest possible volume. 8-2x 8-2x 4. Find the coordinates of the point in the first quadrant on the circle, x+y' =1, so that the rectangle in the figure below has the largest possible area. x3 + y=1 (x, y) 5. Find the radius and height of the cylinder that has the largest volume (V = ar h) if the sum of the radius and height is 9