Can you me with question 8,9,10,14

What basic trigonometric identity would you use to verify that csc x sec x cot x = csc^(2)x

Ricardo ran the 400 meter race 3 times his fastest time was 54.3 seconds his slowest time was 56.1 seconds if his average time was 55.0 seconds what was his time for the third race

Julius sold five times as many computers as sam sold last year. in total, they sold 78 computers. how many computers did julius sell?