[tex]\large\boxed{\pink{\sf \leadsto The \ Volume \ of \ water \ needed \ to \ be \ filled \ is \ 192,500 cm^3}}[/tex]
Given that , cylindrical vessel is 70 cm high and the radius of its base is 35cm . it contains some water up to the height of 20 cm .
And we need to find the water required to fill it completely .
Figure :-
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Let us take the Volume of Cylinder be V and the volume of cylinder filled be v . Let the volume required to be filled be X .
From the figure it's clear that , Volume of water required to fill the cylindrical vessel completely will be :-
[tex]\tt:\implies v + x = V \:\: \bigg\lgroup \red{\bf As \ per \ our \ assumption }\bigg\rgroup \\\\\tt:\implies x = V - v \\\\\tt:\implies x = \pi r^2 H - \pi r^2 h \\\\\tt:\implies x = \pi r^2 ( H - h ) \\\\\tt:\implies x = \pi r^2 ( 70 cm - 20 cm ) \\\\\tt:\implies x = \dfrac{22}{7} \times (35 cm)^2 \times 50 cm \\\\\tt:\implies x = \dfrac{22\times 35 cm \times 35 cm }{7} \times 50 cm \\\\\underline{\boxed{\red{\tt \longmapsto Volume_{fill } = 192,500 cm^3}}}[/tex]