I am not sure exactly what you are looking for is this problem. Are you given choices from which to choose?
The empty set is a set with no numbers. Therefore, you should look for a set that doesn't have any elements.
Answer:

Step-by-step explanation:
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The given equation is

Here we have to solve for n. First we need to get rid of the denominators and for that we do cross multiplication .

Now we need to isolate n. And for that we need to get rid of 12, by dividing both sides by 12



And that's the required value of n .
Answer:
9 gallons of water per minute
Step-by-step explanation:
First identify what you know:
1) The pipe was flowing water for eight minutes.
2) In that eight minutes, 72 gallons of water came out.
So, if 72 gallons of water came out in eight minutes, how many gallons flowed out in a single minute? Well, assuming that the flow rate was consistent, then simply divide the total number of gallons that flowed out, by the number of minutes the pipe was open!
72/8 = 9
The pipe released 9 gallons of water per minute, thus resulting in 72 gallons of water in 8 minutes!
Hope this helps! :)