Numpy: Is there any simple way to solve equation in form Ax = b such that some x's takes fixed values

Question

So basically I want to solve Ax = b but I want the value of x1 to always be equation to say 4.

For example, if A is 3x3 and x is 3x1 then the answer of the above equation should be in form x = [4, x2, x3]

Answer 1

if always x1=4, then x1 is no longer a unknown --> insert x1=4 in each place of the system and simplify the equations (algebraically = manually) --> you will get a system where A is 2x2 and x is 2x1.