Design a cylindrical riser with length$-$to$-$diameter ratio $=2\mathrm{.}0$ is to be designed for a sand casting mold. The casting part is shown below; the units are inches. If the mold constant in Chvorinov$$s rule $=31\mathrm{.}7$ min$/$in$2$ and n $=2,$ find the dimensions of the riser $($diameter and length$)$ so that the riser will take $90$ seconds longer to freeze than the casting part itself.