Rockmaster,
<div class="price">1900</div>
<div class="discount">43%</div>
<script>
let divs = document.querySelectorAll('.price, .discount');
let [price, discount] = [...divs].map(({textContent : n}) => parseFloat(n));
let calc = price * (1 - discount/100)|0;
let out = document.createElement('output');
out.value = calc;
divs[0].after(out);
</script>