Answer:
You still need to wait two hours.
Step-by-step explanation:
So first of all we need to calculate the total volume.
Which is b.h.d.
so here it's:
1m.2m.0,6m= 1,2m³
+
(1m.2m.(1,4m-0,6m))/2=(2m.1m.0,8m)/2=(1,6m³)/2=0,8m³
=2m³
Then it goes down 20cm in 30 min. so that means it cleared
1m.2m.0,2m=0,4m³
2m³/0,4m³=5
So you need 5 times 30 min to clear up the whole volume.
Since you have already cleared it once now you need to do it 4 more times.
4.30min.=2h
