54 \(_{eight}\) and 67\(_{eight}\) = 1438

  Starting with normal addition, 4 + 7 gives 11

  (it is more than the base, 8) 8 goes in 11 just 1 time, remaining 3, the remainder will be written, and the 1 will be added to the sum of 5 and 6 which gives 12 altogether, 8 goes in 12 one time remaining 4, the remainder 4 was written and then the 1 that was the quotient was then written since nothing to add the 1 to.

  So answer is 143 in base eight