A dam $on$ a river $is$ built $so$ that the wall facing the water $is$ shaped like the region

above the curve $y=0\mathrm{.}7x^4$ and below the line $y=1401000\frac{(kg)}{m^3},$ and the acceleration $of$ gravity $is9\mathrm{.}8\frac{(m)}{se{c}^2}.$