Solution: If there are X books on science and technology, there are (3x+ 12) books on literature and art..

(3x+ 12)-x= 156

2x+ 12= 156

2x= 156- 12

2x= 144

X= 144 divided by 2.

x=72

The library bought 72 science and technology books.

Hope to adopt and consult ~ ~ I wish you progress in your study and progress every day ~ ~ ~