(a) Sodium chlorate crystals are easy to grow in the shape of cubes by allowing the solution of water and sodium chlorate to evaporate slowly. If $V$ is the volume of such a cube with side length $x$, calculate $dV/dx$ when $x = 3$ mm. [Explain what this means.]

(b) Find the rate of change of the volume of the cube with respect to its edge length when the surface area of the cube is 14 square mm.

(a)$V'(3)=$ cubic mm/ mm
(b)$V'(?)=$ cubic mm/mm