The molecular mass of nitrogen is 14
and given that it is 28% by weight
let the weight of compound be x 
therefore weight of nitrogen= \frac{28}{100}x
now given that there are two atoms of nitrogen
i.e. \frac{ \frac{28x}{100} }{14}=2 \\ x=100  
now let the molecular mass of metal be M
given that metal is 72% by weight
therefore weight of metal= \frac{72x}{100} \\  =\frac{72*100}{100} \\ =72
now given that there are three atoms of metal
i.e.  \frac{72}{Z}=3 \\ Z=24  
now,equivalent weight = \frac{molecular mass}{charge}
there are two charge on metal
therefore,Equivalent weight of metal= \frac{24}{2}
                                                   =12 ans....................
1 1 1
u know the solution
no my brother told me
sory but i m asking to skaranveer
yeah ,brother
and my name is karanveer singh
(a) 12 is  the equivalent weight of the metal.