Here is the tutorial.
Step 1
Start Solidworks in Part Mode.
Step 2
Front Plane>>Sketch.
Step 3
Make a profile like this.
Step 4
Extrude it by 40mm.
Step 5
Under Features tab choose reference geometry>>plane.
Step 6
Choose the face1 and distance be 20mm.
Step 7
Choose Plane1>>Sketch.
Step 8
Choose Line tool.
Step 9
Standard Views>Normal to.
Step 10
Make a line coincident with both the corners.
Step 11
Insert>>Features>>Rib.
Step 12
Isometric View.
Step 13
Keep the default settings and click OK. Now the rib feature has been created.