How many litres are equivalent to 12 US gallons?

Hint: We first find the relation between US gallons and litres. The measurement is not so common in measurement units. We find the litre value as 3.78541 being equal to 1 US gallons. We use the unitary system, to find the volume of the 12 US gallons in litre by multiplying 12 with 3.78541.

Complete step by step answer:
We need to convert the volume by changing its unit from US gallons to litres.
We find the relation between US gallons and litres where we have 1 US gallons equal to 3.78541 litres.
We already have that in the unitary system. The unitary method is a method in which we find the value of a unit and then the value of a required number of units. The unitary method is also used to find the value of a single unit from a given multiple.
We need the equivalent volume of 12 US gallons.
We multiply 12 with 3.78541 to get the volume which will be equal to 12 US gallons.
Therefore, 12 US gallons is equal to $ 12\times 3.78541=\text{45}\text{.425} $ litres. (approx.)
12 US gallons is equivalent to 45.425 litres.

Note:
 A gallon is a unit of measurement for volume and fluid capacity in both the US customary units and the British Imperial systems of measurement. This unit is not used in the normal or common measurement units. It can also be changed to cubic centimetres using the relation 1 litre being equivalent to 100 cubic centimetres.