SOLUTION: Solve the system: {4x1+x2=7 {12x1+3x2=21 [x1]=[]+s[] [x2]=[]+s[]

In this assignment, the second equation is 3 times first equation.


So, actually, two equations of the given system are equivalent to one equation

    4x + y = 7.


The solution for this equation is

    y = 7 - 4x.


It means that  'x' is a "free variable", which may have any value;
then the corresponding  'y'  value is calculated as  7 - 4x.


In parametric form, we put  

    x = s,

    y = 7 - 4s.


Thus we get the parametric solution to the given system of equations 
in the form, which is requested in the assignment.