In Amplitude Modulation, the amplitude of the carrier wave is varied in accordance with the information signal.What is meant by modulation index?

In Amplitude Modulation, the amplitude of the carrier wave is varied in accordance with the information signal.A message signal of frequency 10 kHz and peak value of 10 V used to modulate a carrier of frequency 1 MHz and peak voltage of 20 V. Determine the modulation index.