A) Total number of old plans = 3500 + 4700 = 8200
In the new month, the unlimited plans increased by 55%, which adds
0.55 • 3500 = 1925
unlimited plans, while the limited plans decreased by 25%, which subtracts
0.25 • 4700 = 1175
limited plans. Then
Total number of new plans = (3500 + 1925) + (4700 - 1175) = 8950
which corresponds to a percent change of
(8950 - 8200)/8200 ≈ 0.0915 = 9.15%
That is, percent change is given by
(new value - old value) / (old value)
B) The percent change is positive, so it's a percent increase.