To solve this problem it is necessary to apply the concepts of Work. Work is understood as the force applied to travel a determined distance, in this case the height. The force in turn can be expressed by Newton's second law as the ratio between mass and gravity, as well
[tex]W = mgh[/tex]
Where,
m = mass
h = height
g = Gravitational constant
When it ascends to the second floor it has traveled the energy necessary to climb a height, under this logic, until the 4 floor has traveled 3 times the height h of each of the floors therefore
[tex]h = 3h[/tex]
Replacing in our equation we have to
[tex]W = mgh\\W = mg(3h)\\W = 3mgh[/tex]
The correct answer is 4.