To set up a medium-sized book corner, science and technology books and humanities books need to be X, 130-x respectively.

To form a small book corner, science and technology books and humanities books need y and 80-y respectively.

x+y= 120

130-x+2*(80-y)= 140

x=90.y=30

Your 12 should be 120. I am a student, too. I just did it.

② ③ There are the following.

If you don't understand, please adopt it.

I just dialed the wrong number.