We're considering investing more in the US small business credit card market. Walk me through how you'd estimate the annual card spend in this market and how much interchange revenue issuers can capture.

我们想加大在美国小微企业信用卡市场的投入。你估算一下，这个市场一年的刷卡消费规模大概有多大？发卡行能分到多少交换费？说说你的拆解思路。