90 pounds.
The mean is all the numbers added together and divided by how many numbers there are.
So, we just add a certain number to 72, 60 and 82 and divide it by 4 till we get 76. Since 90 is the answer I'll use that.
72 + 60 + 82 + 90 = 304
Since there are 4 numbers we divide our total by 4.
304 / 4 = 76!
That makes the fourth piece of luggage 90 pounds.
Good luck on the rest of your questions! :D