eivko

<form>
  <input type="number" min="0" name="a" placeholder="a" />
  <input type="number" min="0" name="b" placeholder="b" />
  <input type="number" min="0" name="c" placeholder="c" />
  <input type="number" min="0" name="qt" placeholder="Количество коробок" />
	<div class="calc-result"></div>
	<input type="button" name="send" value="Рассчитать" />
</form>