Please solve number 17 and 18 please

#16 A box with a square base and an open top must have a volume of 256 cubic inches. Find the dimensions of the box that will minimize the amount of material used (the surface area). #17 A farmer wishes to enclose a rectangular plot using 200 m of fencing material. One side of the land borders a river and does not need fencing. What is the largest area that can be enclosed