"her students to put two spoonfuls of seawater into their containers"
We have then:
(2) * (5) = 10 mililiter
"he gives each of her 22 students a container"
Thus,
(22) * (10) = 220 mililiter
Therefore, they will remain:
(0.4 * 1000) - 220 = 400 - 220 = 180 milliliter
Answer:
There will be left 180 mililiter of seawater after all 22 students have filled their containers