回答: 難問解けたらjustInCaseのBBQに無料ご招待！ https://www.wantedly.com/projects/289455

bbq.py

from urllib.request import *
from urllib.parse import *
import json
import base64
from sympy import *

q = 'W1t4LCAxXV1AW1sxLCAtODcuNjcwNV0sWy04Ny42NzA1LCA0OTc1LjQwNDQxXV1AW1t4XSwgWzFdXQ%3D%3D'

formula = base64.b64decode(unquote(q)).decode('utf-8')
x = Symbol('x')
r = solve(eval('@'.join('Matrix({})'.format(m) for m in formula.split('@'))))

GOOGLE_MAPS_API_KEY = '******************************************'
req = Request('https://maps.googleapis.com/maps/api/geocode/json?latlng={},{}&key={}'.format(r[0][x], r[1][x], GOOGLE_MAPS_API_KEY))
with urlopen(req) as res:
    print(json.load(res)['results'][0]['address_components'][0]['short_name'])

出力: JR 大井町駅