A circular concrete conduit $(n=0\mathrm{.}013)$ is to be laid to carry $25\mathrm{.}8$ cfs of water when it flows full. The conduit drops $0\mathrm{.}15$ ft for every $100$ ft of length. What conduit diameter $($inches$)$ is required for $($i$)$ full$-$flowing condition $($ii$)$ exactly half$-$full condition?