Answer:
There were 75 robberies in 2013.
Explanation:
Since there was an increase in 2014 of 16% from the year prior, then the value of robberies in 2014 is the value from 2013 plus 16%, so it is 100% + 16% that is 116%. To solve this problem we can use a rule of three in such a way that:
87 robberies -> 116%
x robberies -> 100%
116*x = 87*100
x = 8700/116 = 75 robberies
There were 75 robberies in 2013.