please help solve I will upvote thank you!

Suppose you want to calculate the nth power of a given number a. Suppose you know a (fix it say to 42), but n is an input. Perhaps the first thing you would do is to compute a times a times a etc. for n times. How much time would you spend in this case? (we assume multiplying and addition takes constant time) Can we do better? If yes, how? If not, why not? (hint: divide and conquer)