#### Answer

22.5L is needed for one month.
6 containers should be ordered.
1.5L of chlorine will be left at the end of the month.

#### Work Step by Step

Multiply to find the amount of chlorine needed for 30 days.
$750mL\times30=22,500mL$
Move the decimal to convert mL to L.
$22,500mL=22.5L$
Divide to find the number of 4L containers. Round up to ensure the chlorine does not run out.
$22.5\div4=5.625\approx6$
Multiply to find the total amount in the 6 containers.
$4L\times6=24L$
Subtract to find how much is left over.
$24L-22.5L=1.5L