Дано матрицы.Кроме элементов плюс остальные элементы заменить нулем и создавать новые массивы.найти среднее число — Pascal(Паскаль)

uses crt;
type aa=array[1..3,1..4] of real;
var i,j:byte;
    a,b:aa;s_ch1,s1,s_ch2,s2:real;
    
procedure massif(Var a1:aa;n,m:integer);
begin
for i:=1 to 3 do
for j:=1 to 4 do
if a1[i,j]<0 then
a1[i,j]:=0;
end;
 
procedure srchislo(Var a2:aa;n,m:integer;var s,s_ch:real);
begin
s:=0;
for i:=1 to n do
for j:=1 to m do
s:=s+a2[i,j];
s_ch:=s/(n*m);
end;
 
begin
write('enter elements of massif a');
writeln;
randomize;
for i:=1 to 3 do
begin
for j:=1 to 4 do
begin
a[i,j]:=random(10)-3;
write(a[i,j]:2:0,' ');
end;
writeln;
end;
massif(a,3,4);
write('new massif');
writeln;
for i:=1 to 3 do
begin
for j:=1 to 4 do
begin
write(a[i,j]:2:0,' ');
end;
writeln;
end;
write('the average number of massif a= ');
srchislo(a,3,4,s1,s_ch1);
writeln(s_ch1);
write('enter elements of massif b');
writeln;
for i:=1 to 3 do
begin
for j:=1 to 4 do
begin
b[i,j]:=random(10)-3;
write(b[i,j]:2:0,' ');
end;
writeln;
end;
massif(b,3,4);
write('new massif');
writeln;
for i:=1 to 3 do
begin
for j:=1 to 4 do
begin
write(b[i,j]:2:0,' ');
end;
writeln;
end;
write('the average number of massif b= ');
srchislo(b,3,4,s2,s_ch2);
writeln(s_ch2);
end.