How would I do these two questions, using Grade 12 Calculus knowledge .

C2: A woodworker is constructing a unique jewelry box made out different types of expensive wood. The base length of the box is 3 times its width. The wood used to build the top and bottom costs $10/cm and the wood used to build the sides cost $6/cm?. If the box must have a volume of 500 cm3, find the dimensions of the box that would minimize the cost to build it, and determine that cost. Round the final answers to two decimal places. D2: A hydro cable is laid from a house which is 200 m from the road to a power station which is 600 m down the road from a point directly across from the house. The cost to lay the cable is $12/m from the house to the road and $8/m along the road. What is the least expensive way to lay the cable