Answer
$8 \space L$
Work Step by Step
As per the given statement let us consider $a$ be the amount of solution with quantity of acid 70% and $b$ be the amount of solution with quantity of acid 45%.
Thus,
$a+b=20$ ...(1)
and $0.7a+0.45b=0.6(20)$ ...(2)
From equation (1), we have $a=20-b$
Plug $a=20-b$ in $0.7(20-b)+0.45b=0.6(20)$
$14-0.7b+0.45b=12$
$b=8 \space L$
Hence, the correct answer is $8 \space L$.
