changing symbolic variables in each iteration

I have a problem which is transient process in thermodynamics i am trying to write a code for finding the exit mass.I am starting with 3mpa going 1 mpa with decrease of 250kpa in each iteration.What i want to do is writing one code which takes value from tables i created and solve equations from that specific values. For initial substep it looks like that eqns=[v2==d1(a-1,3)+x*d1(a-1,4),u2==d1(a-1,6)+x*d1(a-1,7),2/v2*(he-u2)==m1*(he-u1),m2==2/v2] but when i try to make that values an array to see all the data and have a generic code i messed up. I wanted to know how i can solve array values in equaiton.