q.rb

#!/usr/bin/env ruby

questions = [
  {
    id: "textfield_13989925",
    question: "First Name:"
  }
]

answers = [
  {
    textfield_13989925: "John"
  }
]

questions.each do |q|
  id = q[:id].to_sym
  answer = answers.find { |a| a[id] }

  if answer
    q.merge!(answer: answer[id])
  end
end

p questions