The final mixture must have equal quantities of alcohol and water (1:1 ratio). This means the total alcohol needed is half of 2.1 litres: $$ \text{Total Alcohol} = \frac{1}{2} \times 2.1 = 1.05 \text{ litres} $$ Let the amount drawn from container A be $x$ litres, and from container B be $y$ litres. $$ x + y = 2.1 \implies y = 2.1 - x $$ The proportion of alcohol in A is $\frac{5}{8}$. The proportion of alcohol in B is $\frac{1}{4}$. The total alcohol equation becomes: $$ \frac{5}{8}x + \frac{1}{4}(2.1 - x) = 1.05 $$ $$ \frac{5}{8}x + \frac{0.525}{x} - \frac{2}{8}x = 1.05 $$ $$ \frac{3}{8}x + 0.525 = 1.05 $$ $$ \frac{3}{8}x = 0.525 $$ $$ x = 0.525 \times \frac{8}{3} $$ $$ x = 0.175 \times 8 = 1.4 \text{ litres} $$