a

We are given a+b+c=395, b+c+d=1001 and aAs stated, d can take on a range of values.
Subtract the two equations:
   b+c+d=1001a+b+c   =395-----------------a      +d=606   or
d=606+a
This isn't the whole story as we also know that aAssuming that a,b,c,d are integers there is a clear upper bound on a: a<130. (If a=131, then b+c=264 ==> b=c=132 but bThere is also a lower bound on a. (Unless a,b,c,d are natural numbers, in which case the lower bound is a>0.) If a<-271 then d becomes too small. e.g. if a=-272, then b+c=667 and the smallest that c can be is 334, but d=334 which contradicts c---------------------------------------------------------------------------
Assuming a,b,c,d are integers then the value of d depends on a ; d=606+a where -272If a,b,c,d are natural numbers then d=606+a where 0---------------------------------------------------------------------------