The correct solution is $321$ kips. Please explain the steps to get to the solution. Thank you.

Consider a $3-$story buildings with a total plan area $BxL.$ In which $B=50ft$ and $L=120ft.$ The a$).$ ge weight of each floor and roof are $110l\frac{b}{f}{t}^2$ and $90l\frac{b}{f}{t}^2,$ respectively. The $36ft-$tall bulining is located in a seismic region with $S_{DS}=1,2g$ and $S_{D1}=0\mathrm{.}6g$ for a building supported on rock, where $g$ is the gravitational acceleration. The structure of the building consists of steel moment frames $($all joints are rigid$)$ that have an $R$ value of $8.$ The importance factor $l=1\mathrm{.}15.$ Determine the total design seismic force $($kips$)$ acting at the base of the building $($ seismic base shear in kips$)$