Word: heard in Romans

How then shall they call on him in whom they have not believed? and how shall they believe in him of whom they have not heard? and how shall they hear without a preacher?

Romans 10:18

But I say, Have they not heard? Yes verily, their sound went into all the earth, and their words unto the ends of the world.

Romans 15:21

But as it is written, To whom he was not spoken of, they shall see: and they that have not heard shall understand.