Place this `[text* text-875 "please indicate if Google search keyword)"] right next to [checkbox* your-country "Google search" "referral" "link" "Advertisement"]
so it will look like this
<p>Where did you hear about us?<br />
[checkbox* your-country "Google search" "referral" "link" "Advertisement"] [text* text-875 "please indacte if Google search key word)"] </p>
or you can do it in radio buttons like this:
<p>Where did you hear about us?<br />
[radio radio-100 class:radio-vertical "referral" "link" "Advertisement" "Google search, please indicate key word"] [text text-388] </p>