1) не поняттен вопрос
2) 15 13 9 3 -5 -15 -27 -41 -57 -75
3) 6
4) for i := 1 to 10 do
    begin
        if (a[i] > 0) then
            a[i] := i
        else a[i] := 0;
        write(a[i], ' ');
    end;

код полностью

var
    a: array[1..10] of integer;
    i, k: integer;

begin
    for i := 1 to 10 do
    begin
        a[i] := 15 - i * (i - 1);
        write(a[i], ' ');
    end;
    writeln;
   
    K := 0;
    for i := 1 to 10 do
        if a[i] < 0 then
            k := k + 1;
    Write(k);
    writeln;
   
    for i := 1 to 10 do
    begin
        if (a[i] > 0) then
            a[i] := i
        else a[i] := 0;
        write(a[i], ' ');
    end;
end.