6r78 = 5119 6 x 82 + r x 81 + 7 x 80 = 5 x 92 + 1 x 91 + 1 x 90 6 x 64 + 8r + 7 x 1 = 5 x 81 + 9 + 1 x 1 384 + 8r + 7 = 405 + 9 + 1
8r = 415 - 391
8r = 24 r = 248 = 3