Total card spend is down 12% month over month, and my boss wants to know which channel is dragging it down. The transaction table records the date, channel, and amount of every transaction. Last month online was 4 million, in-store 5 million, and cross-border 1 million; this month online is 4.1 million, in-store 3.8 million, and cross-border 0.9 million. How would you use SQL to get each channel's change and its contribution to the total decline?