function setup() {
  createCanvas(400, 400);
  background(220);

  let balls = []; // 20 objects
  for (let i = 0; i < 20; i++) {
    // with random position and size (from 10-50)
    // [Your Code Here]

    // random_size / 2 means radius of the circle
    // 0 + random_size / 2, 400 - random_size / 2 maks the boundary of the circle keep inside the box
    random_size = random(10, 50);
    balls.push([
      random(0 + random_size / 2, 400 - random_size / 2),
      random(0 + random_size / 2, 400 - random_size / 2),
      random_size,
    ]);
  }

  drawBalls(balls);
}

function drawBalls(balls) {
  // [Your Code Here]
  for (let i = 0; i < 20; i++) {
    circle(balls[i][0], balls[i][1], balls[i][2]);
  }
}