我想在电子邮件订阅表单中添加一个简单的数学验证码。只需两个随机生成的数字的总和就足够了。你能帮我解决这个问题吗？
这是表单的当前代码：
<form id="sib-form" method="POST" action="https://....." data-type="subscription">
<input class="input" type="text" id="FIRSTNAME" name="FIRSTNAME" autocomplete="off" placeholder="First Name" data-required="true" required />
<input class="input" type="text" id="LASTNAME" name="LASTNAME" autocomplete="off" placeholder="Last Name" data-required="true" required />
<input class="input" type="text" id="EMAIL" name="EMAIL" autocomplete="off" placeholder="Email" data-required="true" required />
<button form="sib-form" type="submit">Subscribe </button>
<input type="text" name="email_address_check" value="" class="input--hidden">
<input type="hidden" name="locale" value="en">
</form>