Find out atomic no., mass no., no. of electron and neutron in an element 20X40?

The correct representation of symbol is ₂₀X⁴⁰ . 
Which means the atomic mass of X is 40 and atomic number of X is 20. 
As atomic number of any element is equal to the number of protons present in it, therefore the number of protons = 20. 
As in a neutral atom, number of electrons = number of protons, therefore the number of electron in element X is also 20. 
Since, atomic mass is the sum of number of protons and neutrons, 
Therefore, 
Atomic mass = number of protons + number of neutrons 
Number of protons = 20, atomic mass = 40 
Hence, number of neutrons = 40 -20
                                            = 20