How many more times was the intensity of the 2011 earthquake in Japan (R = 9.0) than the 2015 earthquake in Nepal (R = 7.8)? (See Exercise 41.)

Data from Exercises 41

Measured on the Richter scale, the magnitude of an earthquake of intensity I is defined as R = log(I/I₀), where I₀ is a minimum level for comparison. What is the Richter scale reading for the 1964 Alaska earthquake for which I = 1,600,000,000 I₀?