These are quarters of a circle cut out of the rectangle, so you need to calculate the surface area of these and deduct them.
The curved corners are the inverse of that, so you need the difference between area of a square and of a quarter of a circle, so then you get the area cut out to make a curved corner and you can deduct that from the rectangle.
As for R, I'm not familiar with this notation, but probably radius of these circles.
These are quarters of a circle cut out of the rectangle, so you need to calculate the surface area of these and deduct them.
The curved corners are the inverse of that, so you need the difference between area of a square and of a quarter of a circle, so then you get the area cut out to make a curved corner and you can deduct that from the rectangle.
As for R, I'm not familiar with this notation, but probably radius of these circles.
Radius 5 is 5 units.
Solution to 1970 is:
30*20-(π5^2/4)-(π10^2/4)-2(2^2-π2^2)
yep, too much thinking to solve this one. LOL