Can someone help me understand thank you

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