A grit chamber generates $8$ m$^3/$d $(2113$ gpd$)$ of grit. The grit is pumped through a $10$ cm $(4$ in$.)$ pipe with two pumps $($one working, one on standby$)$ with the pump cycling on once per hour. How many minutes each hour must the grit pump run to provide a minimum velocity of $1\mathrm{.}2$ m$/$s $(4$ ft$/$s$)$ in the pip