A thin uniform annular disc (see figure) of mass M has outer radius 4R and inner radius 3R. The work required to take a unit mass from point P on its axis to infinity is

A

$$\frac{2GM}{7R}(4\sqrt{2} - 5)$$

B

$$-\frac{2GM}{7R}(4\sqrt{2} - 5)$$

C

$$\frac{GM}{4R}$$

D

$$\frac{2GM}{5R}(\sqrt{2} - 1)$$