How to write code to determine the total volume of nested balls?

Question

Delphi

Determine the total volume (in liters) of 12 nested balls with walls of 5 mm. The inner diameter of the inner ball is 10 cm. Consider that the balls are inserted into each other without gaps. What to add to make it work?
part of the code: (I entered the variables d-ball diameter, Pi-pi number, V-volume, i-walls of balls 5 mm.)

var
d, V, z, Pi, i : real;
k : integer;
begin
  i := 0.5;
  d := 10;
  Pi := 3.14;
  for k := 1 to 12 do
  begin
    d := d + i;
  end
  V := Pi * ((d * d * d) / 6);
end

Answer 1

Do you mean wall volume? Then, if we invest without gaps, we get a large ball with a wall of 12 * 5 mm and a door like a small one - 10 cm.
We get an outer diameter of 22cm (10 holes + 2 * 6 walls).
Volume = whole volume - hole volume.
Well, do not forget that a liter \u003d 1 dm ^ 3. Units of measurement must be given accurately.

Answer 2

const
  PI = 3.1415926;
var
  D, V: real;
  k: integer;
begin
D := 10;
V := 0;
for k := 1 to 12 do begin
  V := V + PI * D * D * D / 6;
  D := D + 1;
end
V := V / 1000;

Answer 3

There is no need for such non-optimal algorithms.
Those. You don't have to count the volume every time.
You have no gaps between the walls of all 12 balls. those. can be considered as a total volume. We have:
inside a spherical cavity with a diameter of 10 and 12 layers with 5 cm walls, i.e. each new layer increases the diameter by 10.
Thus . you have an outer diameter = 10 + 10 * 12 = 130
Next, we calculate the volume by the outer diameter and subtract the volume of the cavity (the same formula but by the inner diameter)
No cycles - no need.