Own work. A small cuboid box has a rectangular base of length 3x cm and width x cm, where x>0. The height is y cm, where y>0. The sum of the length, width and height is 20 cm. [9 marks]
Write down an expression for y in terms of x. [1 mark]

The volume of the box is V cm^3. Find an expression for V in terms of x.

Find dv/dx

Find the value of x for which V is a maximum ​