Pop-Art

1. Start by constructing a rectangle with a fill and no stroke.

2. This is the rectangle:not the Live Corner Widgets circled in red.

3. By clicking and pulling gently on a widget you can change the corners of the rectangle. The rectangle below had all the corners modified at once.

 4. To change ONE corner at a time, you need to click on the corner anchor point to select it (with the direct selection tool, the white arrow) and then pull the widget. On the one below the top left hand corner has been modified only.

 5. If you double-click on the widget with the direct selection tool (white arrow), the corners dialog box opens.
Below shows the Corners dialog box open with the radius set at 20mm.

6. There are three different corners to chose from (round, inverted round and chamfer). Experiment to select the most appropriate. Rounding refers to the shape of the corners, relative extends the corners and make them slightly more rounded.
7. The two rounded corners of the start of my B is shown below.

8. Place the circles where the holes will be. Adjust them by eye.

9. Select all three objects. Using the pathfinder panel, select the Minus Front tool.

10.  The result of the B is below.