Draw the right angles on the rotated square. 2B is actually a quadrant. Each semicircle is 4B. Step 1: find area of half a square. Step 2: find the area of semicircle (also 4B). Step 3: find area of triangle (also half a square). There are 4 shaded parts in total. To find 2 of them, take area of half a square - area of triangle - 2B. To get all 4 parts, multiply previous result by 2.