Find r, if 6r7

_{8}= 511_{9}-
**A.**

3 -
**B.**

2 -
**C.**

6 -
**D.**

5

##### Correct Answer: Option A

##### Explanation

6r7_{8} = 511_{9}

6 x 8^{2} + r x 8^{1} + 7 x 8^{o} = 5 x 9^{2} + 1 x 9^{1} + 1 x 9^{o}

6 x 64 + 8r + 7 x 1 = 5 x 81 + 9 + 1 x 1

384 + 8r + 7 = 405 + 9 + 1

391 + 8r = 24

r = (frac{24}{8})

= 3