Someone

cnt = {'2': 2, '3': 1, '4': 7, '5': 4}

tiletypes = {'2': 1, '3': 1, '4': 1, '5': 1}
finalcount = {}

for tile in cnt:
    tiletype = tiletypes[tile]
    finalcount[tiletype] = finalcount.get(tiletype,0) + cnt[tile]

print(finalcount)