Mr ong bought a total of 156 pens and pencils. The ratio of the number of pens to the number of pencils he bought was 4:9. Each pen cost $2. How much did mr ong pay for the pens?
The total ratio representing the number of pens and pencils is 4+9=<<4+9=13>>13.
The cost of pencils is represented by the ratio 9/13, which means 9/13*156=<<9/13*156=108>>108 is the number of pencils Mr. Ong bought.
The cost of pens is represented by 4/13*156=<<4/13*156=48>>48. Answer: \boxed{96}.