feed someone a line
Also, . Cue an actor with his or her next line (or lines), or tell someone what to say, as in Some contestants become tongue-tied, so someone has to feed them a line, or Eric still has trouble learning a part; he needs someone to feed him his lines.
Also, hand someone a line. Lead someone on, deceive with glib or exaggerated talk. For example, He really fed them a line about his important new position, or Don't hand me a line
I know exactly how much you paid for it. [Early 1900s]