Q=600-50t

(2) After 8 hours, how many cubic meters of water are there in the pool?

That is, when t=8, Q=600-50t.

=600-50x8

=600-400

=200

A: Eight hours later, there is still 200 cubic meters of water in the pool.

(3) A few hours later, there is still 100 cubic meter of water in the pool?

There is still 100 cubic meter of water in the pool, which is Q= 100.

At this time 600-50t= 100.

50t=500

t= 10

A: After 10 hour, there is still 100 cubic meter of water in the pool.