Solve the Problem $4.7 \mathrm {~km}$ From Lighthouse a to Port B

Solve the problem.
-It is $4.7 \mathrm {~km}$ from Lighthouse A to Port B. The bearing of the port from the lighthouse is N73 ${ } ^ { \circ } \mathrm { E }$ . A ship has sailed due west from the port and its bearing from the lighthouse is $N 31 ^ { \circ } \mathrm { E }$ . How far has the ship sailed from the port? Round to the nearest tenth of a kilometer.

A) $2.7 \mathrm {~km}$
B) $3.1 \mathrm {~km}$
C) $3.7 \mathrm {~km}$
D) $3.5 \mathrm {~km}$