I need quick help on this. How do I find the missing length?

Aproduction manager test 10 toothbrushes and finds that their mean lifetime is 450 hours. she then design sales package of this type of toothbrush. it states that the customers can expect the toothbrush to last approximately 460 hours. this is an example of what phase of inferential statistics

Prove that 16^4-2^13-4^5 is divisible by 11.

What are the greatest common factor of 75 and 30