Задача с использованием процедур:

const
  nmax = 100;
 
type
  matrix = array[1..nmax, 1..nmax] of integer;
 
var
  f: text;
  a, b, c: matrix;
  i, j, n: integer;
 
procedure creatematrix(var x: matrix; m: integer);
var
  i, j: integer;
begin
  for i := 1 to m do 
    for j := 1 to m do
      x[i, j] := -nmax div 2 + random(nmax);
end;
 
procedure writematrixtofile(var f: text; x: matrix; m: integer);
var
  i, j: integer;
begin
  rewrite(f);
  for i := 1 to m do 
  begin
    for j := 1 to m do
      write(f, x[i, j]:6);
    writeln(f);
  end;
  writeln(f);
  close(f);
end;
 
procedure writematrix(x: matrix; m: integer);
var
  i, j: integer;
begin
  for i := 1 to m do 
  begin
    for j := 1 to m do
      write(x[i, j]:6);
    writeln;
  end;
end;
 
procedure solvematrix(x, y: matrix; m: integer; var z: matrix);
var
  i, j: integer;
  e: matrix;
begin
  for i := 1 to m do 
    for j := 1 to m do 
      if i = j then
        e[i, j] := 1
      else
        e[i, j] := 0;
  for i := 1 to m do 
    for j := 1 to m do
      z[i, j] := x[i, j] * 2 + (y[i, j] + e[i, j]) * 3;
end;
 
procedure readmatrixfromfile(var x: matrix; m: integer);
var
  i, j: integer;
begin
  reset(f);
  for i := 1 to m do 
    for j := 1 to m do
      read(f, x[i, j]);
  close(f);      
end;
 
begin
  assign(f, 'f.txt');
  randomize;
  write('N?');
  readln(n);
  
  creatematrix(a, n);
  writeln('Matrix A: ');
  writematrixtofile(f, a, n);
  readmatrixfromfile(a, n);
  writematrix(a, n);
  
  creatematrix(b, n);
  writeln('Matrix B: ');
  writematrixtofile(f, b, n);
  readmatrixfromfile(b, n);
  writematrix(b, n);
  
  solvematrix(a, b, n, c);
  writeln('Matrix C: ');
  writematrixtofile(f, c, n);
  readmatrixfromfile(c, n);
  writematrix(c, n);
end.