Let x represent the number of fires caused by arson in the previous year.
We were told that it dropped by 17%
Percentage is expressed in terms of 100.
Thus, the amount by which it dropped would be
17/100 * x = 0.17x
Due to this drop, the number of fires caused by arson had dropped to 185. Thus,
x - 0.17x = 185
0.83x = 185
x = 185/0.83
x = 222.892
Rouding to the nearest whole number, the number of fires caused by arson in the previous year is 223