Which of the following actions should you take if a neighbor tells you that your station’s transmissions are interfering with their radio or TV reception?

The first step in resolving any interference complaint is to ensure your own equipment is operating cleanly. If your station is transmitting spurious emissions, it will likely interfere with your own electronics just as it does with your neighbor's. By testing your own TV or radio on the same channels, you can quickly determine if the problem is originating from your transmitter. Contacting the FCC immediately is a drastic overreaction and unnecessary for initial troubleshooting. Furthermore, a "harmonic doubler" is a fictitious distracter; in amateur radio, you want to suppress harmonics, not double them! Making sure your station is functioning properly is the most practical and neighborly first step.