Physics Amplitude-Modulation

[Xenon]

this question is from the International AS/A level Physics book, pg - 428

the question:

A sinusoidal carrier wave has a frequency of 750kHz and an unmodulated amplitude of 4.0V. The carrier wave is to be amplitude-modulated by a sinusoidal signal of frequency 3kHz and the amplitude 0.5V. Describe the modulated carrier wave.

now the answer at the end of the book says the amplitude varies from 3.5V to 4.0V. Can someone explain why this is so and how to u find the maximum and minimum amplitude of a amplitude-modulated wave.

 

[Xenon]

Anyone?

 

[Virtuoso]

the actual amplitude of the modulated wave form should differ from 3.5 to 4.5 as far as i know. this question does not require any calculations. you are provided with the informations only.
in the question the frequency of the carrier wave is 750 khz so the frequency of the modulated wave is also the same..