A twin-engined aircraft can fly 816 miles from city A to city B in 4 hours with the wind and make the return trip in 6 hours against the wind. What is the speed of the wind?

The area of a rectangle is 10 cm^2. one side of the rectangle is x cm. express the perimeter of the rectangle in terms of x and show that this rectangle cannot have a perimeter of 12 cm. the perimeter of the rectangle in terms of x is __ cm