On the surface of planet x a body with a mass of 10 kilograms weighs 40 newtons. the magnitude of the acceleration due to gravity on the surface of planet x is

Based on the Newton's second law of motion, the value of the net force acting on the object is equal to the product of the mass and the acceleration due to gravity. If we let a be the acceleration due to gravity, the equation that would allow us to calculate it's value is,
      W = m x a
where W is weight, m is mass, and a is acceleration. Substituting the known values,
    40 kg m/s² = (10 kg) x a
Calculating for the value of a from the equation will give us an answer equal to 4. 
ANSWER: 4 m/s². 

4m/s^2

I hope this helps!!