I'm confused on how the equation is supposed to work to this question

The intensity levels I of two earthquakes measured on a seismograph can be compared by the formula log = M1 - M2 using the common (base 10) logarithm and where M is the magnitude given by the Richter Scale. In August 2009, an earthquake of magnitude 6.1 hit Honshu, Japan. In March 2011, that same region experienced yet another, more devastating earthquake, this time with a magnitude of 9.0.! How many times greater was the intensity of the 2011 earthquake? Round to the nearest whole number. The intensity of the 2011 earthquake was 5 X times greater than the intensity of the 2009 earthquake