>>13740128ok, math genius here
B = rectangle - circle / 2
A + C = circle - bottom right triangle + B
D - C = upper left triangle - (A + C)
D - C + 2*C = upper left triangle - (A + C) + 2*C
D + C = upper left triangle - (A + C) + 2*C // (D + C is simply B)
B = upper left triangle - (A + C) + 2*C
2*C = upper left triangle - (A + C) - B
C = (upper left triangle - (A + C) - B) / 2