$1.(6$ points$)$ For a flow rate of $1\mathrm{.}3$ m$3/$s$,$ how many rapid sand filters are needed to accommodate a loading rate of $130$ m$3/($d$*$m$2)?$ Each filter bed has a surface area of $12$ m x $12$ m$.$ How should this design be adjusted to accommodate the need to backwash filters $($just comment on needed adjustments, you do not need to provide an adjusted number of filters$)?$