$2\mathrm{.}8$ The cart shown in Fig. P$2\mathrm{.}12\mathrm{.}8$ measures $10\mathrm{.}0$ cm long and $6\mathrm{.}0$ cm high and has rectangular cross sections. It is half filled with water and accelerates down a $20$ incline plane at $a=1\mathrm{.}0\frac{m}{s^2}.$ Find the height $h.$