It should be 19 because originally, it would be 910, but then add 16 more 0's, and 16 + 3 = 19 (and the three is from here -------^)! Check this out ->:https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=91*10%5E17 and https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#safe=strict&q=91000000000... They equal.