Referring to the given circuit, find ZTH if R is 15 kΩ and RL is 38 kΩ.

• 89.82 ∠–51.3° kΩ
• 19.2 ∠–38.3° kΩ
• 9.38∠–51.3° kΩ
• 180 ∠–38.3° kΩ