$ 解：(1)m_水=m_冰=ρ_冰V_冰=0.9\ \text {g/cm}^3×80\ \text {cm}^3=72\ \text {g}$
$ V_水=\frac {m_水}{ρ_水}=\frac {72\ \text {g}}{1\ \text {g/cm}^3}=72\ \text {cm}^3$
$ (2)m_水=ρ_水V_水=1\ \text {g/cm}^3×60\ \text {cm}^3=60\ \text {g}$
$ ρ_{鹽水}=\frac {m_{鹽水} }{V_{鹽水}}=\frac {(13.5+60) g}{70\ \text {cm}^3}=1.05\ \text {g/cm}^3$
