Somebody please help me on this math problem

Astudy of 80 english composition professors showed that they spent, on average, 14.6 minutes correcting a student's term paper. construct and interpret a 90% confidence interval of the mean time for all composition papers. assume that the population standard deviation is 2.9 minutes. round to 1 decimal.

Which of the following statements is true? a. a 10o angle is congruent to a 10o angle. b. a triangle can only have two congruent angles. c. congruent angles always add up to 90o. d. a congruent angle is always 90o.

Marco wrote the equation below. cos ( -π /2) = cos ( 3π / 2) which statement best describes marcos equation?