The mass of the body on moon is 40 kg, What is the weight on the earth

The mass of the object is nothing but the matter present in the object.It remains the same even when the object is taken from one planet to another. Therefore, the mass of the object will remain the same on the surface of the earth as well.
But its weight will change as weight is the gravitational force exerted on the object and the gravitational force is different on different planets.
The weight of the object is given by:

$Weight = Mass\left(M\right) \times Acceleration due to gravity\left(g\right)$

The value of acceleration due to gravity on the earth is approximately 10. 
Therefore, the weight of the object on the surface of the earth will be:

$Weight = 40 X 10 = 400N$