What's the probability of something not happening 6 times?

Simplify 5 square root of 7 end root plus 12 square root of 6 end root minus 10 square root of 7 end root minus 5 square root of 6 . (1 point) 5 square root of 14 end root minus 7 square root of 12 5 square root of 7 end root minus 7 square root of 6 7 square root of 12 end root minus 5 square root of 14 7 square root of 6 end root minus 5 square root of 7

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

Tan198=asin164=? how to solve this? ?