The mass of water required will be approximately [tex] \bf = 555.6\: g [/tex].
[tex]\qquad[/tex] 45g of salt [tex] \sf \longrightarrow[/tex] 100g of H₂O
[tex]\qquad[/tex] 250g of salt [tex] \sf \longrightarrow[/tex] x g of H₂O
[tex]\qquad[/tex] [tex]\red{\twoheadrightarrow\bf45\times x = 250\times 100}[/tex]
[tex]\qquad[/tex] [tex]\twoheadrightarrow\sf45x=25000[/tex]
[tex]\qquad[/tex] [tex]\twoheadrightarrow\sf x=\cancel{\dfrac{25000}{45}}[/tex]
[tex]\qquad[/tex] [tex]\red{\twoheadrightarrow\bf x = 555.6\:g}[/tex]
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