Lets start by making the question a bit simpler, we have two units both with per second in them, so we can get rid of that bit. We are now left with:
How do you conver 5.620 cubic metres into...
1 cubic meter = 35.3146667 cubic feet.
So, simply multiply 6.615 by 35.314 and you're done.
6.615 m³ = 233.606 ft³
Since both are "per second" no multiplication/division is needed since...