Final answer:
An engineer with an engineer's license, along with three years of actual boiler operating experience, would be allowed to take the exam for a first-class engineer license.
Step-by-step explanation:
An engineer with an engineer's license, along with three years of actual boiler operating experience verified by one or more affidavits, would be allowed to take the exam for a first class engineer. This is because the requirements for engineering licensure vary from state to state, and becoming a first class engineer usually involves a combination of education, experience, and passing an examination. With the necessary qualifications, an engineer can apply for a first class engineer license and take the exam to obtain it.