The bearing of B from A is 245, what is the bearing of A from B?

The value of $x$ is:

If the bearing of B from A is $\theta$, then the bearing of A from B (the back bearing) is given by $\theta \pm 180^\circ$. If $\theta > 180^\circ$, subtract $180^\circ$. If $\theta < 180^\circ$, add $180^\circ$.

The bearing of B from A is $245^\circ$. Since $245^\circ > 180^\circ$, we subtract $180^\circ$.

Bearings are typically expressed with three digits.
The bearing of A from B is:

QUESTION 6. Two ships are sailing in the sea on the two sides of a lighthouse. The angle of elevation of the top of the lighthouse is observed from the ships are $30^\circ$ and $45^\circ$ respectively. If the lighthouse is $100 \text{ m}$ high. What is the distance between the two ships?

Let $H$ be the height of the lighthouse, $H = 100 \text{ m}$.
Let $d_1$ be the distance from the first ship to the base of the lighthouse.
Let $d_2$ be the distance from the second ship to the base of the lighthouse.
The total distance between the ships is $D = d_1 + d_2$.

For the first ship (angle of elevation $30^\circ$):

For the second ship (angle of elevation $45^\circ$):

Recall $\tan(30^\circ) = \frac{1}{\sqrt{3}}$ and $\tan(45^\circ) = 1$.

Using $\sqrt{3} \approx 1.732$:

The distance between the two ships is approximately: