<select id="option">
<option value="1.7">start</option>
<option value="2.3">medium</option>
<option value="3.3">advanced</option>
<option value="7">pro</option>
</select>
const projectionScenarioInput = document.querySelector('#option')
// тут обработчик клика по селектору
projectionScenarioInput.addEventListener('change', calculateReturns)
// тут формула расчета
function calculateReturns (e) {
const totalCustomers = parseInt(totalCustomerBaseInput.value)
const projectionPercent = parseFloat(projectionScenarioInput.value)
const mRR = totalCustomers / 100 * projectionPercent *30
const roi = mRR / 30
if (projectionPercent == 1.7) {
aRRContainer.innerHTML ="$" + (totalCustomers + (roi * 15)).toFixed(1)
}
// тут сами расчеты и потом вывод значений
<form id="mainForm" name="mainForm">
<input type="radio" name="option" value="1"> Раз
<input type="radio" name="option" value="2"> Два
<input type="radio" name="option" value="3"> Три
</form>
const projectionScenarioInput = document.querySelector('input[name="option"]')
projectionScenarioInput.addEventListener('change', calculateReturns)
const projectionScenarioInput = document.querySelectorAll('input[name="option"]')
projectionScenarioInput.addEventListener('change', calculateReturns)
projectionScenarioInput.addEventListener('change', calculateReturns)
<form id="mainForm" name="mainForm">
<input type="radio" name="rate" value="1"> Раз
<input type="radio" name="rate" value="2"> Два
<input type="radio" name="rate" value="3"> Три
<input type="number" name="amount" id="amount>
</form>
<span id="roi"></span>
<span id="aRR"></span
<span id="mRR"></span>
<script>
const totalCustomerBaseInput = document.querySelector('#amount')
const projectionScenarioInput = document.querySelector('input[name="rate"]')
const mRRContainer = document.querySelector('#mRR')
const aRRContainer = document.querySelector('#aRR')
const roiContainer = document.querySelector('#roi')
totalCustomerBaseInput.addEventListener('keyup', calculateReturns)
projectionScenarioInput.addEventListener('change', calculateReturns)
function calculateReturns (e) {
const totalCustomers = parseInt(totalCustomerBaseInput.value)
const projectionPercent = parseFloat(projectionScenarioInput.value)
const mRR = totalCustomers / 100 * projectionPercent *30
const aRR = mRR * 12
const roi = mRR / 30
mRRContainer.innerHTML = "$" + mRR.toFixed(2)
aRRContainer.innerHTML = "$" + aRR.toFixed(2)
roiContainer.innerHTML = "$" + roi.toFixed(2)
}
</script>