Could you solve Test 6, Section 4, number 18 for me? Thanks!

Test 4 Section 4 Number 17. Could you give me the explanation for this problem? Thank you!

Test 5, Section 4, Questions 25 and 28. How do you get to the answers?

Test 5, Section 4, Question 20. How do you get to the answer?

Practice test 5, Section 3, Prob 15: How would you think through this problem to get the right answer?