6r7\(_8\) = 511\(_9\) 6 x 8\(^2\) + r x 8\(^1\) + 7 x 8\(^0\) = 5 x 9\(^2\) + 1 x 9\(^1\) + 1 x 9\(^0\) 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 = \(\frac{24}{8}\) = 3