A soil stratum has two layers a 4m-thick dry sand underlain by a 5m–thick saturated sand. Dry unit weight and saturated unit weight of sand are respectively 16.21 KN/m3 and 20.88 KN/m3. How high in m...

A soil stratum has two layers a 4m-thick dry sand underlain by a 5m–thick saturated sand. Dry unit weight and saturated unit weight of sand are respectively 16.21 KN/m3 and 20.88 KN/m3. How high in m should the GWT rises from the top of the saturated sand layer so that
the effective stress at the bottom of that same layer is 104 kPa?