Which algebraic expression represents “the difference of 54 and a number”? HELP I AM TIMED ASAP

School has 204 sixth grade students. if the sixth grade is 30% of the total school, how many students are in the middle school?

Neoli is a nurse who works each day from 8: 00 am to 4: 00 pm at the blood collection centre. she takes 45 minutes for her lunch break. on average, it takes neoli 15 minutes to collect each sample and record the patient's details. on average, how many patients can neoli see each day?

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