As stated by Scott, you can "Create Edges" in Contour Mode from the right-click menu. Go through the blue door-like icon to get there. You'll see a blue outline around all of the geometry and any cuts that have been made.
From there, you can create a horizontal and vertical line where you've drawn the rectangles that intersect. After that fillet the two lines with the radius that you need. You can save the geometry for the next identical part by clicking on the Save icon. I'd save it to the Patterns folder. You'll need to delete all of the geometry with the exception of the arc, the horizontal, the vertical and the angled line. So the lines representing the sides and back of the cabinet need to be deleted. Next go back through the green door icon. Right-click, the choose Cut/Pocket using Closed Contour.
Overall, there may be more steps in this method, but I think it is harder and possibly more error prone to create the two rectangles and the circle exactly where you want them. By using "Create Edges", you've generated all of the end points and can draw construction lines from there that you can work with. There is no math, so less mistakes. While I said, there may be more steps, there are a lot of step to create each rectangle.
In general, if the way you did it works, then you accomplished what you wanted. There are generally many ways to complete a task. Each of us is different and thinks through our projects differently.