Question $2(2\mathrm{.}5$ pts$)$: A coastal project considers a rubble$-$mound breakwater with a slope of $20$ degree. One of the most important elements is the armor units. Determine the size of the elements using Hudson's Formula. The client would like to know the size $(D_{50})$ and weight of rocks $)=(3$ and concrete armor units $)=(10$ which would be necessary to provide stability to the breakwater. Consider the density of water as $1025k\frac{g}{m^3},$ the density of granite rocks as $2650k\frac{g}{m^3}$ and the density of concrete as $2560k\frac{g}{m^3}.$ The depth at the toe of the breakwater is $7m.$ The wave of design in deep waters has a significant height of $H_{\frac{1}{3}}=3\mathrm{.}5m,$ a period of $15s$ and an incidence angle ${}_0=20.$