



 
Hi Christopher. Examine the sequence (n, units digit of 23^{n}): So it repeats: 1, 3, 9, 7, 1, 3, 9, 7, 1, ... The period is 4 units. Use the same principle to discover the sequence and period for 67^{89}. Then add the two units digits together to find your final answer. Hope this helps,  


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