<div id="inputs-box">
  <input type="number">
  <input type="number">
  <input type="number">
</div>
<a href="javascript:void(0)" id="add-input-btn">добавить поле</a>
<h2 id="result-box">Результат: 0</>
input {
  padding: .5em 1em;
  margin: .5em 0;
}

#inputs-box {
  width: 100%;
  max-width: 200px;
  display: flex;
  flex-direction: column;
}
const addInputBtn = document.getElementById('add-input-btn');
const inputsBox = document.getElementById('inputs-box');
const resulBox = document.getElementById('result-box');

addInputBtn.addEventListener('click', e => {
  let inpt = document.createElement('input');
  inpt.type = 'number';
  
  inputsBox.appendChild(inpt);
})

inputsBox.addEventListener('input', e => {
  let sum = 0;
  
  inputsBox.querySelectorAll('input').forEach(el => sum += +el.value)
  
  resulBox.textContent = `Резульат: ${sum}`;
})

External CSS

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External JavaScript

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