A chemist needs 10 liters of a $25 \%$ acid solution. The solution is to be mixed from three solutions whose concentrations are $10 \%, 20 \%$, and $50 \%$. How many liters should the chemist use to satisfy the following
a) Use as little as possible of the $50 \%$ solution.
$10 \%$ concentration solution in liters
$20 \%$ concentration solution in liters
$50 \%$ concentration solution in liters
b) Use as much as possible of the $50 \%$ solution.
$10 \%$ concentration solution in liters
$20 \%$ concentration solution in liters
$50 \%$ concentration solution in liters
c) Use 2 liters of the $50 \%$ solution.
$10 \%$ concentration solution in liters
$20 \%$ concentration solution in liters
$50 \%$ concentration solution in liters