Please explain

For each of the circles, the area, say X, is πr^2.

So the shaded region is clearly more than half (even if it is not upto scale, we know that the OP is the length of the radius. So circle at P passes through O and curves away, so if you draw a diameter at circle O perpendicular to line OP, you can see that the shaded region will be a semicircle plus some area where the other circle curves away.) So area of shaded region will be “X/2 + something”. So twice the area will be “X + something”

Quantity B us just X