In the given question it is already mentioned that a 64 gallon tank contains 45 gallons of oil. Out of the 45 gallons 4/5 th of the quantity is sold. It can be said that the full tank capacity of 64 gallons is of no use to the problem.
Now getting to the equation part of the problem.
Quantity of oil removed = (4/5) * 45 gallons
= (4 * 9) gallons
= 36 gallons.
So it can be said that 36 gallons of oil from the total of 45 gallons has been sold.
