What is -0.4 as a fraction or mixed number in simplest form?

Ineed to learn how to solve this problem

Using the quadratic formula find the zeros of the given polynomial -5x^2+3x-11

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