47. A rectangle has perimeter 20 m. Express the area of the rectangle as a function of the length of one of its sides.
48. A rectangle has area 16 m . Express the perimeter of the rectangle as a function of the length of one of its sides.
49. Express the area of an equilateral triangle as a function of the length of a side.
50. Express the surface area of a cube as a function of its volume.
51. An open rectangular box with volume 2 m has a square base. Express the surface area of the box as a function of the length of a side of the base.