How to make true horizontal easy step with photoshop

Have a picture not horizontal, do this with photoshop,

 

This picture not in horizontal position,..

 

1. First step, select "ruler tool" on the tool bar

 

2. Step number 2, just like this screenshot draw the tool to the horizontal line

3. go to image menu select rotation and point to arbitary, klick that you would see rotate window just OK to rotate that horizontal

4. i think you have done, like this pic