Twenty Thousand A Month

A thumbnail service serves 240 million images per day, averaging 34 KB each, straight from origin servers. Egress from origin to the internet costs $0.085 per GB. Your provider's CDN costs $0.020 per GB delivered to users, and origin egress into the CDN is billed at the normal $0.085 per GB.

You put the CDN in front and measure a 94 percent cache hit rate. Using $1\text{ GB} = 10^9$ bytes and a 30 day month, what is the new monthly egress bill?