[tex]\begin{gathered} \text{Let's K is the ratio of body's mass to the water mass.} \\ So,\text{ k=}\frac{90}{60}=1.5 \\ So\text{, the mass of water in 75 kg person is } \\ \Rightarrow m=\frac{75}{k}=\frac{75}{1.5}=50\operatorname{kg} \end{gathered}[/tex]
