Answer
July: increase of 3.9
August: decrease of 0.3
September: decrease of 6.3
October: decrease of 18.2
November: decrease of 15.7
December: decrease of 10.3
Work Step by Step
July: $33.6-29.7=3.9$
August: $33.3-33.6= -0.3$
September: $27.0-33.3= -6.3$
October: $8.8-27.0= -18.2$
November: $-6.9-8.8= -15.7$
December: $-17.2- (-6.9)= -10.3$