// Bunny Ears
private int ears = 0;

public int bunnyEars(int bunnies) {
  if (bunnies > 0) {
    ears += 2;
    bunnies--;
    bunnyEars(bunnies);
  }

  return ears;
}

//////////////////////////////////////

// Triangle
int total = 0;

public int triangle(int rows) {
  if (rows == 0) {
    return total;
  }

  else {
    total += rows;
    rows--;
    triangle(rows);
  }

  return total;
}