=3a？ - 1

Question 2: Original formula =4b-6a-6a+9b.

= 13b- 12a

Question 3: The original formula =14abc-28a+18a-6abc.

=8abc- 10a

Question 4: Original formula =5ab-[2a? b-(3ab-4ab？ +a？ b)

=5ab-(2a？ b-3ab+4ab？ -a？ b

=5ab-2a？ b+3ab-4ab？ +a？ b

=8ab-a？ b-4ab？

Question 5: Original formula =2a? -[-3a-(4a？ -3a？ +a+a-a？ )]

=2a？ -(-3a-a-a)

=2a？ +5a

Question 6: I wonder if the topic is 4a? -【a？ +(4a？ -2a)-2(a？ -3a)]？ Yes, that's how it was solved.

Original formula =4a? -(a? +4a？ -2a-2a？ +6a)

=4a？ -3a？ -4a

=a？ -4a

Please contact me if you still don't understand.