I have Math Destroyer (1st edition 2010). On question 17 on Practice Test 4, there is no "-" symbol in front of 3x. 😕 Maybe you read the question wrong or you have a different version of destroyer?
for your first question: there is no "-" symbol in front of 3x and the answer is A. the question asks you to simplify the expression. for the second question:
sqrt(8) = sqrt(4*2)=sqrt(4)*sqrt(2)=2sqrt(2)