Afixed amount used as a standard of measurement is called

Students are given 3 minutes for each multiple-choice question and 5 minutes for each free-response question on a test. there are 15 questions on the test, and students are given 51 minutes to take it.how many multiple-choice questions are on the test?

Can someone me with #s 8, 9, and 11. with just one of the three also works. prove using only trig identities.

What unit of been sure would be appropriate for the volume of a sphere with a radius of 2 meters