37 GNP: Let's assume it's Sirius. Remove 4 ep and 4 culture and you're at 29. At a 1.4 modifier (say, Pottery) that means 20+1 bpt. Of those 20 you get 8 from the palace and 1 from the city center, leaving 11 for tiles. We know they are working a coastal fish for 3, leaving 8 for the other two tiles. Presumably one of those is an improved precious metal tile.
Note that this is likely the only configuration that could reach 37 GNP. If it was any team other than Sirius, it would be 31 from research, which is not possible at a 1.4 modifier. 22 base gives 30 net, 23 base gives 32 net.