Milk 90 L: Water = 70 L
Let the quantity of milk and water in the vessel initially be \( M \) and \( W \), respectively. We know:
\[ M + W = 160 \]
Out of the total milk, 70% is retained, and after removing 55% of the mixture:
\[ 0.3M + 0.7W = 0.45 \times 160 = 72 \]
Now, we have the system of equations:
\[ M + W = 160 \quad \text{(1)} \]
\[ 0.3M + 0.7W = 72 \quad \text{(2)} \]
Multiply equation (1) by 0.3:
\[ 0.3M + 0.3W = 48 \quad \text{(3)} \]
Subtract equation (3) from equation (2):
\[ (0.3M + 0.7W) - (0.3M + 0.3W) = 72 - 48 \]
\[ 0.4W = 24 \quad \Rightarrow \quad W = 60 \]
Substitute \( W = 60 \) into equation (1):
\[ M + 60 = 160 \quad \Rightarrow \quad M = 100 \]
Thus, the quantity of milk is 100 L and the quantity of water is 60 L.