For the following step you will need a grid every 1px. Go to Edit > Preferences > Guides & Grid and enter 1 in the Gridline every box. Pick the Rectangle Tool (M), create a 250 by 1px shape, and fill it with R=191 G=185 B=162.
Select this shape and go to Object > Transform > Move. Enter the data shown below then click on the Copy button. This will create a copy right below the selected shape. Now fill it with white.