Statistics (empirical rule)

Hi all, I've been stuck on this problem on my statistics study guide (I have an exam tomorrow morning)Here a link to the graph (it's about average talk time on cell phones): http://ift.tt/2taDVBW question: what proportion of cell phone batteries have talk time between 438 and 534 minutes? My study guide answer says: 0.68 + 0.135 = 0.815 I understand they got the 0.68 from the empirical rule of the one standard deviation is 68%, but where did the 0.135 come from?Another similar question: what proportion of cell phone batteries have talk time between 534 and 566 minutes? The answer is 0.0235. I just don't know how to get there.I emailed my professor and she was absolutely no help. Thanks in advance! via /r/cheatatmathhomework http://ift.tt/2scWurF