A circle has radius x cm. What is the area of a sector of the circle with angle 135°, leaving the answer in terms of x and π?

• A.\( \frac{\pi x^2}{8} \)
• B.\( \frac{3\pi x^2}{8} \)
• C.\( \frac{5\pi x^2}{8} \)
• D.\( \frac{3\pi x}{8} \)