Problem 45338. Area-04

Asif, Thanks for another nice problem.
I think the description would be improved if it said the "red shaded portion", because there are two shaded portions in the drawing.

The main challenge at this point is solving the problem without the image. The code below illustrates my understanding of the problem, but if you want an added challenge, try figuring out what to compute from the test suite.

clear; close all
figure; hold on
a = 7; b = 2;
t = linspace(0,2*pi); xi = b*cos(t)/2; eta = b*sin(t)/2; indx = find(t>=pi/2 & t<=3*pi/2);
plot([0 a a 0 0],[0 0 b b 0],'k')
plot((a-b)/2+xi,b/2+eta,'k',(a+b)/2+xi,b/2+eta,'k')
fill([0 0 (a-b)/2 (a-b)/2+xi(indx) (a-b/2) 0],[0 b b b/2+eta(indx) 0 0],'r')
axis equal; set(gca,'XTick','','YTick','','XColor','w','YColor','w')