Initial ratio of milt to water $ = 4:1$
So, if $4x$ amount of milk is there, $x$ amount of water is there.
Let $y$ be the amount of water added. Now, the ratio changes to $4:3.$ i.e., for $4x$ amount of milk, now there is $3x$ amount of water. So, we get that $y = 2x.$
In $14l,$ amount of water $= \frac{3}{3+4} \times14 = 6l$
Given, $\frac{4x+6}{3x-6} = \frac{5}{3}$
$\implies 12x + 18 = 15x -30$
$\implies x = 16$
$y = 2x = 32.$