Area of shaded region = (area of square FGHJ) - (area of sector FGJ)

(area of square FGHJ
Since each side of the square has length x, the area = $x^2$

area of sector FGJ
Area of sector = $(\frac{n}{360})(\pi)(radius^2)$, where $n =$ the central angle

Since FGHJ is a square, we know that the central angle (angle GFJ) $= 90°$
We also know that the radius $= x$
So, the area of sector FGJ $= (\frac{90}{360})(\pi)(x^2)= (\frac{1}{4})(\pi)(x^2)=$ $\frac{\pi x^2}{4}$

Area of shaded region = $x^2$ $-$ $\frac{\pi x^2}{4}$

= $\frac{4x^2}{4}$ $-$ $\frac{\pi x^2}{4}$

= $\frac{4x^2 - \pi x^2}{4}$

We get:
Quantity A: $\frac{4x^2 - \pi x^2}{4}$

Quantity B: $\frac{x^2}{4}$

Multiply both quantities by $4$ to get:
Quantity A: $4x^2 - \pi x^2$
Quantity B: $x^2$

Divide book quantities by $x^2$ to get:
Quantity A: $4 - \pi$
Quantity B: $1$

In other words we have:
Quantity A: $4 - 3.14 = 0.86$
Quantity B: $1$

Answer: B